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Title: The applied side of Bell nonlocality
Date/Time: 27-Apr, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Since its formulation in 1964, Bell's theorem has been classified under "foundations of physics". Ekert's 1991 attempt to relate it to an applied task, quantum cryptography, was quenched by an approach that relied on a different basis and was allegedly equivalent. Ekert's intuition was finally vindicated with the discovery of "device-independent certification" of quantum devices. In this colloquium, I shall revisit the tortuous history of that discovery and mention some of the subsequent results. Some references that review this topic: V. Scarani, Acta Physica Slovaca 62, 347 (2012) [https://arxiv.org/abs/1303.3081] N. Brunner et al., Rev. Mod. Phys. 86, 419 (2014) [https://arxiv.org/abs/1303.2849] S. Pironio et al., New J. Phys. 18, 100202 (2016) [http://iopscience.iop.org/1367-2630/focus/Focus-on-Device-Independent-Quantum-Information]
Title: Quantum Physics: A Possible Theory of the World as a Whole
Date/Time: 23-Mar, 04:00AM
Venue: CQT Seminar Room, S15-03-15
Abstract: Quantum mechanics is commonly said to be a theory of microscopic things: molecules, atoms, subatomic particles. Most physicists, though, think it applies to everything, no matter what the size. The reason its distinctive features tend to be hidden is not a simple matter of scale. Over the past few years experimentalists have seen quantum effects in a growing number of macroscopic systems. The quintessential quantum effect, entanglement, can even occur in large systems as well as warm ones - including living organisms - even though molecular jiggling might be expected to disrupt entanglement. I will discuss how techniques from information theory, quantum and statistical physics, can all be combined to elucidate the physics of macroscopic objects. Can it be that part of the macroscopic world is quantum, while the rest is, in some sense, classical? This question is also of fundamental importance to the development of future quantum technologies, whose behavior takes place invariably in the macroscopic non-equilibrium quantum regime. I will discuss the concept of quantum macroscopicity and argue that it should be quantified in terms of coherence based on a set of conditions that should be satisfied by any measure of macroscopic coherence. I will show that this enables a rigorous justification of a previously proposed measure of macroscopicity based on the quantum Fisher information. This might shed new light on the standard SchrÃ¶dinger cat type interference experiment that is meant to demonstrate the existence of macroscopic superpositions and entanglement.
Title: 17th Asian Quantum Information Science Conference
Date/Time: 04-Sep, 12:00AM
Venue: Shaw Foundation Alumni House, NUS
Welcome to the 17th Conference on AQIS The AQISâ€™17 conference focused on quantum information science, an interdisciplinary field bridging quantum physics, computer science, mathematics, and information technology. AQISâ€™17 is the 17th conference in a series that includes EQISâ€™01-EQISâ€™05 and AQISâ€™06-AQISâ€™16. AQISâ€™17 consist of invited talks, selected oral and poster presentations, tutorials. Contributions were solicited in (but not limited to) the following areas: â—¾Quantum computation, algorithms and complexity â—¾Quantum information theory â—¾Techniques for suppressing decoherence â—¾Quantum cryptography â—¾Quantum communications experiments and theory â—¾Implementations of quantum information processing â—¾Quantum processor and computer design Tutorial speakers: â—¾Peter HÃ¸yer (Calgary) â—¾Charles Bennett (IBM, USA) Invited speakers: â—¾Shalev Ben-David (University of Maryland, USA) â—¾Masahito Hayashi (Nagoya, Japan & NUS, Singapore) â—¾Zhengfeng Ji (UTS, Sydney, Australia) â—¾Mio Murao (Tokyo, Japan) â—¾Stefano Pironio (Brussels, Belgium) â—¾William Slofstra (Waterloo, Canada) â—¾Jian-Qiang You (CSRC, Beijing) â—¾Henry Yuen (Berkeley, USA)
Title: Mini-Workshop on Post-Quantum Cryptanalysis
Date/Time: 18-Mar, 12:00AM
Venue: SPMS-MAS-03-06 (Executive Class Room 1), NTU
Mini-Workshop on Post-Quantum Cryptanalysis Jointly organized by School of Physical & Mathematical Sciences, Nanyang Technological University and Centre For Quantum Technologies, National University of Singapore Synopsis: The workshop addresses recent advances on (quantum-) cryptanalysis (security assessment) pertaining to complexity-theoretic platforms under consideration as possible underpinnings for upcoming industry standards on post-quantum cryptography. In particular, our focus is on two of the most prominent ones, namely for lattice-based- and code-based public-key cryptosystems. Date: March 18, 2017 Venue: SPMS-MAS-06 (Executive Class Room 1), NTU Organizers: Divesh Aggarwal (Centre For Quantum Technologies, National University of Singapore) Ronald Cramer (CWI, Amsterdam & Mathematisch Instituut, Leiden University) Miklos Santha (Universite Paris VII & Centre For Quantum Technologies, National University of Singapore) Chaoping Xing (School of Physical & Mathematical Sciences, Nanyang Technological University) Speakers Jung Hee Cheon (Seoul National University) Antoine Joux (Laboratoire d'informatique de Paris 6) Noah Stephens-Davidowitz (New York University) Jean-Pierre Tillich (INRIA Paris) Nguyen Ta Toan Khoa (Nanyang Technological University) Program 9:30-10:30 Speaker: Antoine Joux Title: Revisiting lattice reduction with interval arithmetic 10:30-11:00 Tea Break 11:00-12:00 Speaker: Noah Stephens-Davidowitz Title: Pseudorandomness of ring-LWE for any ring and modulus 12:00-13:30 Lunch break 13:30-14:30 Speaker: Jung Hee Cheon Title: Hardness of NTRU and its related problems 14:30-15:00 Tea Break 15:00-16:00 Speaker: Nguyen Ta Toan Khoa Title: Lattice-based group signatures: achieving full dynamicity with ease 16:00-17:00 Speaker: Jean-Pierre Tillich Title: A survey of code-based public-key cryptography To register, click here
Title: From a single particle to many-body quantum physics and its application workshop, Singapore
Date/Time: 15-Feb, 12:00AM
Venue: Botanique Room, Park Alexandra Hotel, Singapore
General Information From a single particle to many-body quantum physics and its application workshop, will be held at the Park Hotel Alexandra, Botanique Room on 15 to 17 Feb 2017. Precision measurements and quantum many body physics play vital role in our understanding of fundamental physics as well as its application. This workshop is meant to discuss the physics of a few to many body quantum systems as well as their application towards metrology and fundamental physics understanding. The workshop jointly organized by the Max Plank Institute for Nuclear Physics, Germany and the Centre for Quantum Technologies, Singapore aims at bringing researches working on these topics together so as to find common platform for future collaboration and also strengthen the existing ones. Needless to mention that the workshop unlike a conference format will keep more time for informal discussions while having structured presentations as the central theme of the workshop. The workshop is co-sponsored by the Max Planck Society, Germany, National University of Singapore and Nanyang Technological University, Singapore. Registration Deadline: 26 January 2017 (all timezone) Organising Committee Klaus Blaum, Max Planck Institute for Nuclear Physics, Germany Rainer Dumke, CQT, NUS and NTU, Singapore Manas Mukherjee, CQT, NUS, Singapore Secretariat Contact Evon Tan (Singapore) Centre for Quantum Technologies National University of Singapore Block S15, room #03-18 3 Science Drive 2 Singapore 117543 Phone : +65-6516-7019 Fax : +65-6516-6897 Email: cqtthme@nus.edu.sg Gabriele Weese (Germany) Max Planck Institute for Nuclear Physics, Germany Saupfercheckweg 1 D-69117 Heidelberg Germany Phone : +49- (0)6221-516 851 Fax : +49- (0) 6221-516 852 Email: sekretariat.blaum@mpi-hd.mpg.de
Title: International Frontiers of Quantum and Complexity Science, Singapore
Date/Time: 08-Jan, 12:00AM
Venue: Hotel Fort Canning, Singapore
Title: Quantum Engineering Science and Technologies Symposium (QuESTS) 2016, Singapore
Date/Time: 14-Nov, 12:00AM
Venue: University Town Plaza, Auditorium 1 NUS, Singapore
Title: Quantum-Safe Crypto Workshop 2016, Singapore
Date/Time: 03-Oct, 12:00AM
Venue: Level 3 Seminar Room, CQT, Singapore
Title: International Conference on Quantum Communication, Measurement and Computing (QCMC) 2016, Singapore
Date/Time: 04-Jul, 12:00AM
Venue: University Town Stephen Riady Centre, NUS, Singapore
About QCMC 2016 The International Conference on Quantum Communication, Measurement and Computing (QCMC) was established in 1990 to encourage and bring together scientists and engineers working in the interdisciplinary field of quantum information science and technology. To date, twelve such meetings have been held and the thirteenth will take place 4-8 July, 2016 in Singapore. It will be organised by the Centre for Quantum Technologies (CQT), National University of Singapore Scope of the conference * Cryptography and Communications * Measurement and Metrology * Quantum Computing and Information Theory * Implementations * Quantum Simulations * Quantum Control * Foundations of Quantum Physics
Title: Workshop SU(N), gauge fields and cold atoms, Singapore
Date/Time: 18-Jan, 12:00AM
Venue: Level 3 Seminar Room, CQT, Singapore
Title: The 22nd International Conference on Laser Spectroscopy, ICOLS 2015, Singapore
Date/Time: 28-Jun, 12:00AM
Venue: Shangri-La's Rasa Sentosa Resort & Spa, Singapore
Title: Quantum Symposium, NUS, Singapore
Date/Time: 26-Mar, 12:00AM
Venue: University Hall Auditorium and CQT Seminar Room, Singapore
General Information The Centre for Quantum Technologies and the British High Commission's Science and Innovation Team are pleased to announce a Quantum Symposium to be held 26-27 March in Singapore at the Centre for Quantum Technologies, NUS Campus. The co-organised event will bring together leading researchers in quantum technologies from the UK and Singapore, with the goal of exploring collaboration opportunities and increasing scientific links between the two countries. Singapore's long-term investment in the Centre for Quantum Technologies and the UK's launch of a national Quantum Technologies Programme highlight the countries' commitment to research in this field. The event will showcase UK and Singapore capabilities and research excellence in quantum technologies. Topics to be discussed includes: * Communications * Cryptography * Computations * Sensors * Metrology * Imaging List of Speakers Edward A Hinds, Imperial College, London, UK Mete Atature, University of Cambridge, UK Murray Barrett, Centre for Quantum Technologies, NUS, Singapore Steve Beaumont, University of Glasgow, UK Rainer Dumke, Centre for Quantum Technologies, NUS and NTU, Singapore Peter Kruger, The University of Nottingham, UK Christian Kurtsiefer, Centre for Quantum Technologies, NUS, Singapore Alexander Ling, Centre for Quantum Technologies, NUS, Singapore John Morton, University College London, UK Jeremy O'Brien, University of Bristol, UK Tim Spiller, The University of York, UK Ian Walmsley, University of Oxford, UK Venue 26 March, Thursday University Hall Auditorium Level 2, University Hall, Lee Kong Chian Wing Find on google maps 27 March, Friday CQT Level 3 Seminar Room Science Drive 2, Block S15-03-15 Contact Us Evon Tan (Secretariat) Centre for Quantum Technologies National University of Singapore Block S15, room #03-18 3 Science Drive 2 Singapore 117543 Phone : +65-6516-7019 Fax : +65-6516-6897 Email: cqtthme@nus.edu.sg
Title: UMI Kick-off meeting, University Hall, NUS, Singapore
Date/Time: 19-Jan, 12:00AM
Venue: NUS, CQT, Singapore
Title: Workshop on Quantum Contextuality, WQC 2014, Singapore
Date/Time: 03-Nov, 12:00AM
Venue: Level 3 Seminar Room, CQT, Singapore
Title: Theory of Quantum Computation, Communication and Cryptography, TQC 2014
Date/Time: 21-May, 12:00AM
Venue: Ngee Ann Kongsi Auditorium, ERC, University Town, NUS
General Information The 9th Conference on the Theory of Quantum Computation, Communication and Cryptography, will be held at the Ngee Ann Kongsi Auditorium, University Town, National University of Singapore from 21-23 May 2014. It will be organised by the Centre for Quantum Technologies (CQT), National University of Singapore Quantum computation, quantum communication, and quantum cryptography are subfields of quantum information processing, an interdisciplinary field of information science and quantum mechanics. The TQC conference series focuses on theoretical aspects of these subfields. The objective of the conference is to bring together researchers so that they can interact with each other and share problems and recent discoveries. It will consist of invited talks, contributed talks, and a poster session. Areas of interests includes, but is not limited to: * Quantum algorithms * Models of quantum computation * Quantum complexity theory * Simulation of quantum systems * Quantum cryptography * Quantum communication * Quantum estimation and measurement * Quantum noise * Quantum coding theory * Fault-tolerant quantum computing * Entanglement theory
Title: Beyond I.I.d 2014
Date/Time: 19-May, 12:00AM
Venue: Global Learning Room, ERC, University Town, NUS
General Information Beyond I.I.d in information theory will be organised by the Centre for Quantum Technologies (CQT), National University of Singapore, from 19-21 May 2014 at the University Town, Education Resource Centre, Seminar Room on NUS campus. Information theory has a very large range of applications in physics. However, the use of established information-theoretic techniques often relies on the i.i.d. assumption, which demands that certain processes (e.g., the use of a communication channel) can be repeated an arbitrary number of times identically and independently of the other invocations. In order to overcome this limitation, researchers have recently started to devise a more general theory of information, non-asymptotic information theory, which enables the study of arbitrary, structureless settings. Recent topics of interest in this area include explicit one-shot bounds on operational quantities, finite blocklength analysis, second order coding rates, the information spectrum method, and new techniques to derive strong converses. Although this generalised theory is still under development, it has already found a variety of applications, ranging from cryptography and communication theory to thermodynamics and statistical mechanics. The goal of the workshop is to bring together researchers who work on various approaches to this general theory of information and their applications. This workshop is a follow-up on the workshop "Beyond i.i.d. in Information Theory" that was held in Cambridge, 8-11 January 2013 (Beyond i.i.d. 2013). A particular goal of this second edition of the workshop is to foster exchange between the classical and quantum information theory communities. Organisers Marco Tomamichel, CQT, NUS (Chair), Vincent Tan, ECE and Math, NUS, Stephanie Wehner, CQT, NUS Contact Us Evon Tan (Secretariat) Centre for Quantum Technologies National University of Singapore Block S15, room #03-18 3 Science Drive 2 Singapore 117543 Phone : +65-6516-7019 Fax : +65-6516-6897 Email: cqtthme@nus.edu.sg
Title: BergeFest 2014
Date/Time: 22-Apr, 12:00AM
Venue: Ngee Ann Kongsi Auditorium, ERC, University Town, NUS
About Berge Fest "In celebration of B.G. Englert's contributions to Quantum Information, Quantum Optics, and the Foundations of Quantum Mechanics." This conference has two purposes. The first is to discuss recent work in the broad area of quantum information theory, quantum optics and foundations of quantum mechanics. This includes e.g. work on non-classical light, open driven quantum systems, estimation & discrimination of quantum states, quantum tomography, the classical-quantum boundary, quantum many-body systems, interferometry and the foundations of quantum physics, and generally work whose purpose is to discover, understand, and apply quantum concepts and ideas. Applications of these concepts to quantum information, in particular to quantum computing and quantum cryptography, will also be covered. The second purpose is to celebrate the 60th birthday of Berge Englert. Berge's work in recent years has focused on the above topics, and with this conference we would like to honor both his contribution to physics and him as a person. Oral presentation at this workshop is for invited speakers only. Organisers: Janos Bergou (Hunter College of the CUNY) Hans Briegel (University of Innsbruck and IQOQI) Kwek Leong Chuan (NIE, NTU, and CQT, NUS) Ng Hui Khoon (Yale-NUS College, and CQT, NUS) Han Rui (CQT, NUS) This event is jointly organised with the Institute of Advanced Studies, NTU.
Title: IPS 2014 Meeting
Date/Time: 26-Feb, 12:00AM
Venue: Town Plaza, University Town, NUS
Title: Quantum Computing Workshop on Inverse Moment Problem
Date/Time: 09-Dec, 12:00AM
Venue: Institute for Mathematical Sciences, NUS
Overview Applications of moments of measures in polynomial optimization led to a number of breakthroughs in optimization and real algebraic geometry, as well as to better understanding of ways to encode measures. Other similar threads are recently seen in the theory of intergation on polytopes and counting of integer points in polytopes, as well as in quantum computing. The aim of the program is to further investigate relations between these topics and inverse moment problems, i.e., questions of reconstructing measures from a set of its moments, which are traditionally attacked by purely analytic tools. Organizing Committee Co-Chairs â€¢Dmitrii Pasechnik (Nanyang Technological University) â€¢Sinai Robins (Nanyang Technological University) Members â€¢Jean B. Lasserre (LAAS-CNRS) â€¢Monique Laurent (Centrum Wiskunde & Informatica) â€¢JesÃºs De Loera (University of California at Davis) â€¢Mihai Putinar (Nanyang Technological University) â€¢Le Hai Khoi (Nanyang Technological University) â€¢Claus Scheiderer (UniversitÃ¤t Konstanz) â€¢Boris Shapiro (Stockholm University) â€¢Stephanie Wehner (National University of Singapore) Activities â€¢Optimization, Moment Problems and Geometry I (Conference/Workshop/Tutorials): 27 Nov - 6 Dec 2013 & 11 Dec 2013 â€¢ Quantum Computing Workshop on Inverse Moment Problem (organized by S. Wehner): 9 - 13 Dec 2013 â€¢ Optimization, Moment Problems, and Geometry II (Conference/Workshop): 16 - 27 Dec 2013 â€¢ Graduate Student Winter School/Workshop, Featuring Mini-Courses by A. Leykin, J. Stoyanov and J. Yu*: 16 - 24 Dec 2013 â€¢ Polyhedra, Lattices, Algebra, and Moments (Conference/Workshop/Tutorials): 7 - 16, 23 Jan 2014 â€¢Public Lecture Date: Tuesday, 17 Dec 2013 Venue: LT31, Block S16, Level 3, Faculty of Science, National University of Singapore, Singapore 117546 6:30pm - 7:30pm A Walk Down the Arithmetic-Geometric Mean Streets of Mathematics Bruce Reznick, University of Illinois at Urbana-Champaign, USA * Our office will be closed on Wednesday, 25 Dec 2013 and Wednesday, 1 Jan 2014, being Singapore public holiday. Students and researchers who are interested in attending these activities are requested to complete the online registration form. The following do not need to register: â€¢ Those invited to participate. â€¢Those applying for financial support.
Title: Mathematical Horizons for Quantum Physics 2
Date/Time: 12-Aug, 12:00AM
Venue: Institute for Mathematical Sciences, NUS
Overview Quantum theory is one of the most important intellectual developments in the early twentieth century. Since then there has been much interplay between theoretical physics and mathematics, both pure and applied. Arguably, the field of Mathematical Physics, equally at home in mathematics and in physics, emerged from John von Neumannâ€™s seminal work on the spectral theory of linear operators in Hilbert space which was triggered by the birth of quantum theory in the mid 1920s. Yet this is just one historical example of how the mathematical insights and tools that are developed in the course of answering challenging mathematical questions arising from physical problems have contributed to the advance of both mathematics and physics. In this tradition, it is the objective of this IMS Programme to bring together Mathematicians, whose work has a bearing on quantum physics, with researchers in Mathematical Physics and Theoretical Physics, whose work will benefit from the mathematical progress. The collaboration between these scientists of different background, different expertise, and different scientific culture will bear fruit on the research of all participants by intellectual cross-fertilization. The first programme on Mathematical Horizons in Quantum Physics (MHQP-2008) was held at IMS from 28 July to 21 September 2008, under the overarching theme of Operator Theory and Operator Algebra Theory. In this second installment of the MHQP series, we turn to the rich areas of many-body open quantum systems and quantum information theory. Today, much interest in various fields of Mathematical Physics is devoted to the study of open quantum systems, whose properties are profoundly affected by environment, for instance through the continuum of decay channels. Moreover, every finite fermion system has its own characteristic features, resonance and threshold phenomena are generic; they are great interdisciplinary unifiers. In MHQP-2013, we will bring together scientists working on different many-body open quantum systems with people working on quantum information theory, to stimulate interdisciplinary contacts and contribute to the exchange of ideas. Activities The Programme will consist of four overlapping three-week Sessions, each devoted to a selected topic. Session 1 will focus on Quantum Information Theory, which has much overlap with the realm of Mathematical Physics. This links closely to Information-Theoretic Approaches to Thermodynamics, which is the topic of Session 2. Session 3 will focus on mathematical aspects of Many-Particle Systems, and Session 4 will deal with Open Quantum Systems. Programme Structure: Each Session has a Session Organizer who is in charge of defining the Session and the selection of the Discussion Leaders and the participants. At the start of each Session, there will be presentations by the Discussion Leaders to lay the groundwork. There follows an intense period of about 20 days of discussions and close collaborations among the participants. The Session ends with talks summarizing the progress accomplished and a round-table discussion defining future problems and areas of close collaboration. â€¢Session 1 on Quantum Information Theory, 12 - 30 Aug 2013 (Week 1 - 3) Session Organizers: Burkhard KÃ¼mmerer (Technische UniversitÃ¤t Darmstadt) and Hans Maassen (Radboud University Nijmegen) - Programme for NUS Graduate Students (QT5201H), 12 Aug, 15 Aug, 19 Aug 2013 (Week 1 - 2) The talks will consist of an introductory part, and a part which is meant to hint at the new directions which the speakers feel should be explored during the workshop. Both parts are relevant for NUS graduate students, who will later on take a test in order to get their credit points. For a description of the three themes, click HERE. - Topic 1: Entanglement of multipartite and infinite systems (ENTANGLEMENT) Discussion Leader: GÃ©za Giedke (Max Planck Institute Garching) - Topic 2: Spaces of operators, not necessarily operator algebras (OPERATOR SPACES) Discussion Leader: Marius Junge (University of Illinois at Urbana-Champaign) - Topic 3: Cones of positive maps on operator algebras (POSITIVE CONES) Discussion Leader: Erling StÃ¸rmer (University of Oslo) â€¢Session 2 on Information-Theoretic Approaches to Thermodynamics, 26 Aug - 13 Sep 2013 (Week 3 - 5) Session Organizers: Stephanie Wehner (National University of Singapore), Renato Renner (ETH Zurich), and Jens Eisert (Freie UniversitÃ¤t Berlin) Discussion Leaders: Stephanie Wehner (National University of Singapore), Renato Renner (ETH Zurich), and Jens Eisert (Freie UniversitÃ¤t Berlin) â€¢Session 3 on Many-Particle Systems, 9 - 27 Sep 2013 (Week 5 - 7) * Our office will be closed on Tuesday, 24 Sep 2013 for a department outing Session Organizer: Jakob Yngvason (UniversitÃ¤t Wien) - Topic 1: Many-body systems in random potentials Discussion Leader: Jakob Yngvason (UniversitÃ¤t Wien) - Topic 2: Strongly correlated fermion systems Discussion Leader: Manfred Salmhofer (UniversitÃ¤t Heidelberg) - Topic 3: Bose-Einstein Condensation Discussion Leader: Robert Seiringer (Institute of Science and Technology Austria (IST Austria)) â€¢Session 4 on Open Quantum Systems, 23 Sep - 11 Oct 2013 (Week 7 - 9) * Our office will be closed on Tuesday, 24 Sep 2013 for a department outing Session Organizer: Robert Alicki (The University of GdaÅ„sk) - Topic 1: Relaxation, transport and stability in complex quantum open systems Discussion Leader: Wojciech De Roeck (UniversitÃ¤t Heidelberg) - Topic 2: Non-Markovianity in quantum open systems Discussion Leader: Sabrina Maniscalco (Heriot-Watt University) - Topic 3: Models of quantum machines Discussion Leader: Robert Alicki (The University of GdaÅ„sk) â€¢ Public Lectures ... Jointly organized with Centre for Quantum Technologies, NUS Date: Thursday, 29 Aug 2013 Venue: LT33, Block S17, Level 2, Faculty of Science, National University of Singapore, Singapore 119260 6:30pm - 7:30pm Quantum Physics, Public and Private Information, and the Lost Literature of Antiquity Charles Bennett, IBM, USA ... Jointly organized with Centre for Quantum Technologies, NUS Date: Tuesday, 10 Sep 2013 Venue: LT31, Block S16, Level 3, Faculty of Science, National University of Singapore, Singapore 117546 6:30pm - 7:30pm Gambling Against the Second Law of Thermodynamics Renato Renner, ETH Zurich, Switzerland Students and researchers who are interested in attending these activities are requested to complete the online registration form. The following do not need to register: â€¢ Those invited to participate. â€¢Those applying for financial support.
Title: Physics Education Seminar
Date/Time: 03-Jun, 12:00AM
Venue: NUS High School
Title: Japan-Singapore Workshop on Multi-user Quantum Networks
Date/Time: 17-Sep, 12:00AM
Venue: Centre for Quantum Technologies, NUS
Japan-Singapore Workshop on Multi-user Quantum Networks Dates: 17th-20th September 2012 Place: CQT Seminar Room, S15-03-15, CQT, NUS, Singapore Co-chairs: Masahito Hayashi, Andreas Winter Secretary: Tan Hui Min Evon This workshop is scheduled after QCRYPT Workshop schedule is available here. Organizer: This workshop will be jointly organized by CQT, National University of Singapore and Japanese research fund Grant-in-Aid for Scientific Research (A) "Project on Multi-user Quantum Network" in cooperation with NICT Commissioned Research, Quantum cryptographic theory (Security certification and efficient key distillation) and Japanese research fund Grant-in-Aid for Scientific Research (A) "Deepening Quantum Protocol Theory". Contact: Masahito Hayashi Email: multiuser@quantumlah.org All talks of the workshop are by invitation only. However, anyone interested may attend, but we are required to send a registration email to multiuser@quantumlah.org. This email should contain the name of the participant(s) as well as the arrival and departure dates. Registration is necessary as the capacity of the workshop venue is limited. Register early to avoid disappointment. Speakers Abroad â€¢Matthias Christandl (ETH Zurich) â€¢Maciej Demianowicz (Gdansk Univ. of Tech.) â€¢Omar Fawzi (McGill Univ.) â€¢Vittorio Giovannetti (NEST, Scuola Normale Superiore) â€¢Min-Hsiu Hsieh (Univ. of Tech., Sydney) â€¢Joe Renes (ETH Zurich) â€¢Ivan Savov (McGill Univ.) â€¢Christian Schaffner (Univ. of Amsterdam & CWI Amsterdam) CQT â€¢Iordanis Kerenidis (CNRS, LIAFA & CQT) â€¢Bill Rosgen (CQT) â€¢Valerio Scarani (CQT) â€¢Marco Tomamichel (CQT) â€¢Stephanie Wehner (CQT) â€¢Andreas Winter (Bristol Univ. & CQT) Japan â€¢Masahito Hayashi (Nagoya Univ. & CQT) â€¢Takeshi Koshiba (Saitama Univ.) â€¢Wataru Kumagai (Tohoku Univ.) â€¢Francois Le Gall (Univ. of Tokyo) â€¢Ryutaroh Matasumoto (Tokyo Institute of Tech.) â€¢Harumichi Nishimura (Nagoya Univ.) â€¢Tomohiro Ogawa (The Univ. of Electro-communications) â€¢Toyohiro Tsutumaru (Mitsubishi Electric.) â€¢Shun Watanabe (Tokushima Univ.)
Title: QCRYPT 2012
Date/Time: 10-Sep, 12:00AM
Venue: Shaw Foundation Alumni House, NUS
Title: Singapore School of Physics - Strong Light-Matter Coupling: from atoms to solid-state systems
Date/Time: 21-May, 12:00AM
Venue: Nanyang Executive Centre, NTU
Title: Quantum Discord Conference 2012
Date/Time: 09-Jan, 12:00AM
Venue: Hotel RE!, Singapore
Quantum Discord Workshop 2012 Quantum discord has captured the attention and imaginations of many researchers working in a variety of (quantum) fields. We are organizing this workshop with the aim of bringing these researchers together to discuss not only quantum discord, rather quantum physics and the role of correlations. We will not have many talks in this workshop, about 4 hours of talks per day. Instead we want to encourage collaboration building and interdisciplinary research pursuits. Quantum discord has had a significant impact in open quantum system, many-body physics and phase transition, quantum communication, computing and information, thermodynamics and demons, measurement problem to list a few fields. Some of these communities are fairly detached from each other and many are geographically separated. We hope that this will be a good opportunity to close these gaps and open new avenues. Programme Discord Workshop Programme Venue The event will take place at Hotel Re! Getting to Hotel Re!: 1. By MRT: take green line from airport (terminal 2) to Outram Parkstation. Walk to hotel in 7 minutes (see map). MRT runs from 6AM to 12AM. Should take about 35 minutes. 2. By Taxi: it will cost about S$20 - S$30 depending on time of the day. The hotel address is Hotel Re! @ Pearl's Hill, 175A Chin Swee Road, Singapore 169879 (nearest MRT is Outram Park) The colloquium will be held at Centre for Quantum Technologies (CQT), Seminar Room (S15 #03-15). You may refer to CQT website for directions. Committees Local Organizers: Kavan Modi (CQT, NUS) Hugo Cable (CQT, NUS) Vlatko Vedral (University of Oxford / CQT, NUS) External Committee: Carlton M. Caves (University of New Mexico, USA) Felipe Fanchini, (Uni. Federal de Ouro Preto, Brasil) Sabrina Maniscalco (Heriot-Watt University and University of Turku) Oh Choo Hiap (CQT, NUS) Andreas Winter (CQT, NUS) Contact Us Kavan Modi Centre for Quantum Technologies National University of Singapore Block S15, room #03-18 3 Science Drive 2 Singapore 117543 Fax : +65-6516-6897 Email: discord@quantumlah.org Participants â€¢ Adesso, Gerardo â€¢ Aghamalyan, David â€¢ Agrawal, Pankaj â€¢ Amico, Luigi â€¢ Aolita, Leandro â€¢ Arruda, Luiz Gustavo â€¢ Assad, Syed â€¢ Attipat, Rajagopal â€¢ Auccaise, Ruben â€¢ Biamonte, Jacob â€¢ Bo, Li â€¢ Bylicka, Bogna â€¢ Chew, Lock Yue â€¢ Chitambar, Eric â€¢ Cornelio, Marcio â€¢ Correa, Luis â€¢ Dakic, Borivoje â€¢ Daniel, Alonso â€¢ Datta, Animesh â€¢ de Oliveira, Marcos â€¢ Devi, Usha A. R. â€¢ Dhar, Himadri Shekhar â€¢ Du, Jiangfeng â€¢ Eastin, Bryan â€¢ Fanchini, Felipe â€¢ Farrow, Tristan â€¢ Fedrizzi, Alessandro â€¢ Fei, Shaoming â€¢ Ficek, Zbigniew â€¢ Giorda, Paolo â€¢ Gu, Mile â€¢ Gurkan, Nilhan â€¢ Hu, Xue-Yuan â€¢ Joag, Pramod â€¢ Joynt, Robert â€¢ Koh, Teck Seng â€¢ Korolkova, Natalia â€¢ Kwon, Younghun â€¢ Laflamme, Raymond â€¢ Lang, Matthias â€¢ Lee, Chee Kong â€¢ Li, Chuan-Feng â€¢ Li, Nan â€¢ Luo, Shunlong â€¢ Lutz, Eric â€¢ Ma, Xiaosong â€¢ Maniscolca, Sabrina â€¢ Mazzola, Laura â€¢ Oppenheim, Jonathan â€¢ Paris, Matteo â€¢ Paterek, Tomek â€¢ Paternostro, Mauro â€¢ Piani, Marco â€¢ Rodriguez-Rosario, Cesar â€¢ Rodriguez, Jeremy â€¢ SaiToh, Akira â€¢ Sen (De), Aditi â€¢ Sen, Ujjwal â€¢ Serra, Roberto â€¢ Shaji, Anil â€¢Shang, Jiangwei â€¢ Son, Wonmin â€¢ Streltsov, Alexander â€¢ Tatham, Richard â€¢ Terno, Daniel â€¢ Vacanti, Giovanni â€¢ Vinjanampathy, Sai â€¢ Walther, Philip â€¢ Wang, Jingbo â€¢ Williamson, Mark â€¢ Wu, Shengjun â€¢ Wu, Yuchun â€¢ Xu, Jin Shi â€¢ Yang, Seungho â€¢ Yu, Sixia â€¢ Zhang, Chengjie â€¢ Zurek, Wojciech
Title: Workshop of Quantum Tomography 2011
Date/Time: 28-Nov, 12:00AM
Venue: Centre for Quantum Technologies, NUS
Workshop on Quantum Tomography Overview: The purpose of WQT@CQT2011 is to gather experts and students working in areas which are related to quantum state/process estimation to discuss interesting and unsolved problems. We hope that new insights and different perspectives will result from these discussions. In view of this objective, this workshop will include only a few talks and more discussion sessions. Main areas of interests: * Quantum state estimation * Quantum process estimation * Experimental tomography * Detectors tomography * Other related topics Programme Monday, 28 November 8:30am Transport depart from Link Hotel to CQT 9:00am Registration at CQT (for those who could not attend the Reception) 9:15am Zdenek Hradil's review of maximum-likelihood methods for state estimation 10:00am Robin Blume-Kohout's review of alternative methods 10:45am Coffee break 11:15am Gerd Leuch's review of experimental state estimation 12:00noon Lunch break 2:00pm Discussion sessions start, possibly in smaller groups - Programme as of 25 October 2011, 1800hr (SG time) Registered Participants â€¢Joonwoo Bae â€¢Janos Bergou â€¢Iva Bezdekova â€¢Jacob Biamonte â€¢Robin Blume-Kohout â€¢Yurii Bogdanov â€¢Maria Chekhova â€¢Matthias Christandl â€¢Joshua Combes â€¢Giacomo Mauro D'Ariano â€¢Jibo Dai â€¢Luiz Davidovich â€¢Thomas Durt â€¢Jens Eisert â€¢Joseph Emerson â€¢Berge Englert â€¢Bruno Escher â€¢Chris Ferrie â€¢Steve Flammia â€¢Christopher Fuchs â€¢Alexei Gilchrist â€¢David Gross â€¢Rui Han â€¢Zdenek Hradil â€¢Amir Kalev â€¢Sergey Kulik â€¢Ruynet L. de Matos Filho â€¢Yink Loong Len â€¢Gerd Leuchs â€¢Yi-Kai Liu â€¢Yin Lu â€¢Dmitri Mogilevtsev â€¢Masoud Mohseni â€¢Alex Monras â€¢Thomas Monz â€¢Pramod Mysore â€¢Hui Khoon Ng â€¢Matteo Paris â€¢Kia Tan, Benjamin Phuah â€¢Vaclav Potocek â€¢Philippe Raynal â€¢Jaroslav Rehacek â€¢Luis Sanchez-Soto â€¢Christian Schuette-Nuetgen â€¢Jiangwei Shang â€¢Bohumil Stoklasa â€¢Takanori Sugiyama â€¢Si Hui Tan â€¢Yong Siah Teo â€¢Mankei Tsang â€¢Peter Turner Local Organisers: Berge Englert (CQT, NUS) Hui Khoon Ng (CQT, NUS, and DSO National Laboratories) Yong Siah Teo (CQT, NUS) Venues: Workshop Venue: Centre for Quantum Technologies, NUS 3 Science Drive 2 S15-03-15 (CQT Seminar Room) Singapore 117543 Accommodation for Workshop participants: Link Hotel 50 Tiong Bahru Road Singapore 168733 http://www.linkhotel.com.sg/ Hotel rooms will be reserved for all overseas participants. Please indicate your travel dates in the registration page. You can email wqt@quantumlah.org should there be any changes. Contact Us Evon Tan (Secretariat) Centre for Quantum Technologies National University of Singapore Block S15, room #03-18 3 Science Drive 2 Singapore 117543 Phone : +65-6516-7019 Fax : +65-6516-6897 Email: wqt@quantumlah.org
Title: The 5th Asia-Pacific Workshop on Quantum Information Science
Date/Time: 25-May, 12:00AM
Venue: Nanyang Executive Centre, NTU
Jointly Organized by Institute of Advanced Studies @ NTU Singapore Department of Physics, NUS Supported by Centre for Quantum Technologies, NUS South East Asia Theoretical Physics Association Institute of Physics, Singapore Asia Pacific Center for Theoretical Physics Quantum Information Science is one of the most dynamic areas of inter-disciplinary research involving a wide range of scientists ranging from physicists to computer scientists to mathematicians and engineers. The fundamental observation in this field is that any computation is essentially a physical process. The current relentless drive towards increasing speed and miniaturization of computers will eventually lead the computer industry into a molecular/atomic domain where seemingly strange quantum behavior takes over from familiar classical notions. Quantum physics offers an entirely new form of computational parallelism that will make quantum computers more powerful than conventional computers by many orders of magnitude. The first Asia-Pacific Workshop on Quantum Information Sciences was organized for the first time in Singapore in 2001. Since then, the workshop and conference have been held at various places in Taiwan, Korea, Australia and China. The workshop will provide an opportunity for the international scientific community to discuss the recent experimental and theoretical developments in all aspects of quantum information science, and the program comprises invited talks and poster presentation. This workshop will also be held in conjunction with a Festchrift for Prof Vladimir Korepin.
Title: The Fourteenth Workshop on Quantum Information Processing - QIP2011
Date/Time: 08-Jan, 12:00AM
Venue: Capella Singapore, Sentosa
QIP2011 Quantum Information Processing (QIP) is a rapidly developing field of research spanning both physics and computer science. As the name implies, the field extends information processing (including computing and cryptography) to physical regimes where quantum effects become significant. QIP 2011 was the fourteenth workshop on theoretical aspects of quantum computing, quantum cryptography, and quantum information in a series that started in Aarhus in 1998 and was held 2010 at ETH Zurich, Switzerland. QIP 2011 featured a tutorial programme, invited talks, contributed talks, and a poster session. In addition, there was a rump session with short informal talks. Plenary speakers: â€¢Fernando BrandÃ£o (Universidade Federal de Minas Gerais, Brazil) â€¢Sergey Bravyi (IBM Yorktown Heights) â€¢Omar Fawzi (McGill University Montreal) â€¢Serge Fehr (CWI Amsterdam) â€¢Andrew Lutomirski (Massachusetts Institute of Technology) â€¢John Martinis (University of California, Santa Barbara) â€¢Ashley Montanaro (University of Cambridge) â€¢Oded Regev (Tel Aviv University) Tutorial Programme: â€¢Patrick Hayden (McGill University Montreal): Quantum information theory via decoupling â€¢Maciej Lewenstein (ICFO Barcelona): Optical lattices and quantum simulations â€¢Ben Reichardt (IQC, University of Waterloo): Quantum query complexity Public Lecture: Charles H. Bennett (IBM Research, USA) gave a public lecture, "Information is Quantum", at Singapore Management University, on Wednesday 12 January, 5pm. News â€¢Videos of the recorded lectures, as well as lecture slides, are available in the scientific programme â€¢Also check out the Photos section for QIP 2011 group photos and contributed conference photos.
Title: Complex Quantum Systems - CQS 2010
Date/Time: 17-Feb, 12:00AM
Venue: Institute for Mathematical Sciences, NUS
Overview The program will concentrate on two topics, (i) Large Coulomb Systems and (ii) Quantum Information and Reduced Density Matrices. The corresponding parts will start with kick-off workshops during the first and third week of the program. The program will be organized in two related sections, but with different emphasis, namely â€œLarge Coulomb Systemsâ€ and â€œQuantum Information and N-Representabilityâ€. The topics of the program will include: â€¢ Effective description of atoms and molecules (density and density matrix functionals, computational aspects) â€¢ Models of relativistic quantum electrodynamics â€¢ Stability of matter (including relativistic systems and the quantized photon field) â€¢ Lieb-Thirring and other Sobolev type inequalities â€¢ Reduced density matrices and the N-representability problem in quantum information theory â€¢ Quantum and Classical Complexity Theory of the N-representability and related physical problems â€¢ Approximation methods for correlated states (Semi-definite programming, Matrix Product States (MPS), Projected Entangled Pair States (PEPS), fermionic PEPS) These topics mark an area of considerable current research activity. The goal of the program is not only to communicate recent research results and initiate collaboration between the mathematicians and physicists that take part in the respective research effort, it is also intended to initiate collaboration between participants of the many-particle community and the quantum information community. Activities The first four weeks will emphasize the theory of Large Coulomb System, the last four weeks (there will be an overlap of two weeks) will emphasize Quantum Information and N-Representability. Each part will start with a kick-off workshop. The first workshop will start February 17, the second on March 1. Each workshop will be followed by working periods on the topics raised during the workshop. As part of the workshops, lead participants will give introductory talks into the current state of research. Also at the beginning of each period, there will be tutorial lectures directed towards graduate students, postdocs, and scientist interested in starting work in the area of large Coulomb systems and quantum electrodynamics, followed by a working and collaboration session of three weeks. The tutorial lectures is planned to consist of five two hour sessions. â€¢ Workshop on the theory of Large Coulomb System: 17 â€“ 19 Feb 2010 â€¢Public Lecture Date: Tuesday, 23 Feb 2010 Venue: LT31, Block S16, Level 3, Faculty of Science, National University of Singapore Singapore 117543 6:30pm - 7:30pm Cold Atoms and Quantized Vortices Jakob Yngvason, University of Vienna, Austria â€¢ Tutorial Lectures i.Mathematical methods and results on multiparticle quantum mechanics: 22 â€“ 23, 25 â€“ 26 Feb 2010 by Rafael Benguria, Pontificia Universidad CatÃ³lica de Chile, Chile ii.Reduced density matrices in atomic physics and chemistry; a variational approach: 24 Feb 2010 by Dimitri Van Neck, Ghent University, Belgium â€¢Informal Workshop on Complex Quantum Information: 1 â€“ 5 Mar 2010 â€¢Informal Discussions: 8 â€“ 12 Mar 2010, 16 â€“ 19 Mar 2010 Students and researchers who are interested in attending these activities and who do not require financial aid are requested to complete the online registration form. The following do not need to register: â€¢ Those invited to participate. â€¢ Those applying for financial support. Venue â€¢IMS Auditorium â€¢Detailed instruction on how to get to the institute by public or private transport Funding for Young Scientists The Institute for Mathematical Sciences has limited funds to cover partial support for travel and living expenses for young scientists interested in participating in the program. Applications should be received at least three (3) months before the commencement of the program. Application form is available in (MSWord|PDF|PS) format for download. More information is available by writing to: Secretary Institute for Mathematical Sciences National University of Singapore 3 Prince George's Park Singapore 118402 Republic of Singapore or email to imssec(AT)nus.edu.sg. For enquiries on scientific aspects of the program, please email Berthold-Georg Englert at cqtebg(AT)nus.edu.sg. Organizing Committee Chair â€¢Heinz Siedentop (Ludwig-Maximilians-UniversitÃ¤t MÃ¼nchen) Members â€¢Matthias Christandl (Ludwig-Maximilians-UniversitÃ¤t MÃ¼nchen) â€¢ Berthold-Georg Englert (National University of Singapore) â€¢Andreas Winter (National University of Singapore and University of Bristol) Visitors and Participants â€¢Overseas visitors â€¢Local visitors â€¢Graduate students â€¢ Registered local participants
Title: Joint CQT-CCRG Workshop on Quantum Error Correction
Date/Time: 23-Feb, 12:00AM
Venue: SPMS-MAS-Executive Classroom 2, NTU
Title: Workshop on Quantum Correlations
Date/Time: 30-Nov, 12:00AM
Venue: Centre for Quantum Technologies, NUS
Workshop on Quantum Correlations 30 November - 4 December 2009 | Venue: Centre for Quantum Technologies, NUS (Singapore) Organised by: Dagomir Kaszlikowski, Tomasz Paterek, Valerio Scarani To discuss about "non-locality" one has to meet locally, and even those who prefer "non-realism" will be really here in Singapore. But these paradoxes (true or fake) will be left for discussions over dinner. The workshop is about the technical advances in the field: dimension witnesses, device-independent cryptography and other tasks, the principles of "information causality" and "macroscopic locality", detection loophole, violation of Bell's inequalities in unusual scenarios... As the nature of the topic demands, the workshop is organized without pre-established agreement: there are no scheduled talks, we shall improvise the plan of informal discussions day-by-day. Schedule | Photo Album Time of discussions: 10am-12noon, 2-5pm. schedule List of confirmed participants â€¢Antonio Acin (ICFO, Barcelona) â€¢Jonathan Allcock (University of Bristol) â€¢Caslav Brukner (University of Vienna) â€¢Nicolas Brunner (University of Bristol) â€¢Roger Colbeck (ETH Zurich) â€¢Borivoje Dakic (University of Vienna) â€¢Rodrigo Gallego (ICFO, Barcelona) â€¢Nicolas Gisin (University of Geneva) â€¢Esther Haenggi (ETH Zurich) â€¢Yeong-Cherng Liang (University of Sydney) â€¢Lluis Masanes (ICFO, Barcelona) â€¢Serge Massar (Universite Libre de Bruxelles) â€¢Miguel Navascues (Imperial College) â€¢Marcin Pawlowski (University of Gdansk) â€¢Stefano Pironio (University of Geneva) â€¢Lana Sheridan (Centre for Quantum Technologies, NUS) â€¢Tamas Vertesi (Atomki, Budapest) â€¢Stephanie Wehner (California Institute of Technology) â€¢Stefan Wolf (ETH Zurich) â€¢Marek Zukowski (University of Gdansk)
Title: Les Houches School of Physics in Singapore Ultracold Gases and Quantum Information
Date/Time: 29-Jun, 12:00AM
Venue: Nanyang Executive Centre, NTU
Title: First Workshop on "Quantum Technology in Biological Systems"
Date/Time: 10-Jan, 12:00AM
Venue: The Sentosa Resort, Singapore
First Workshop on Quantum Technology in Biological Systems 11 - 16 January 2009 | Venue: The Sentosa Resort (Singapore) Organised by: Vlatko Vedral, Elisabeth Rieper The main objective of this multidisciplinary workshop consisting of physicists, chemists and biologists is in the area of quantum biology. The planned location will be on the Sentosa Island in Singapore between 10-17 January 2009. The intention of the workshop is to stimulate a free exchange of ideas in the field of quantum biology that is becoming increasingly more fascinating and diverse. The main question we would like to address is whether nature engages in any kind of quantum information processing. Titles and Abstracts Group Photo Accomodation The Sentosa Resort, Singapore 2 Bukit Manis Road Sentosa Singapore 099891 Tel: +65 6275 0331 Workshop Programme Time Sunday 11 Jan Monday 12 Jan Tuesday 13 Jan Wednesday 14 Jan Thursday 15 Jan Friday 16 Jan 0930 Background in Physics Advanced QM / Photosynthesis What is life?/ Bird Navigation Molecules Closing Discussion Artur Ekert Janet Anders Bruno Sanguinetti Francois Filaux Juan Pablo Paz Valerio Scarani Discussion Simon Benjamin 1030 Coffee break @ Sarong Coffee Corner 1100 Nathan Babcock Nicolas Gisin Wolfgang Wiltschko Judith Klinmann Closing Discussion II Tony Leggett Libby Heaney Vasily Ogryzko 1230 Lunch @ Terrace Restaurant 1400 Philip Walther Richard Cogdell Torsten Ritz Anita Goel Singapore City Tour Frances Wang Grahem Fleming Kiminori Maeda Discussion 1530 Coffee break @ Sarong Coffee Corner 1600 Opening Discussion Sarong Room, The Sentosa Resort Paul Davies Discussion Chris Rodgers Discussion Elisabeth Rieper Discussion Discussion 1800 Night Safari Tour Workshop Dinner 1900 Welcome Dinner 2230 List of confirmed participants â€¢Janet Anders, University College London â€¢Nathan Babcock, University of Calgary â€¢Simon Benjamin, University of Oxford â€¢Richard Cogdell, University of Glasgow â€¢Paul Davies, Arizona State University â€¢Artur Ekert, Centre for Quantum Technologies, NUS â€¢Francois Fillaux, CNRS Thiais â€¢Graham Fleming, UC Berkeley â€¢Nicolas Gisin, UniversitÃ© de GenÃ¨ve â€¢Anita Goel, University of Harvard â€¢Mile Gu, The University of Queensland â€¢Libby Heaney, Centre for Quantum Technologies, NUS â€¢Judith Klinman, University of Berkeley â€¢Tony Leggett, University of Illinois at Urbana-Champaign â€¢Kiminori Maeda, University of Oxford â€¢Vasily Ogryzko, Institute of cancerology Gustave Roussy, Paris â€¢Juan Pablo Paz, Ciudad Universitaria, Buenos Aires â€¢Thorsten Ritz, University of California, Irvine â€¢Chris Rodgers, University of Oxford â€¢Bruno Sanguinetti, University of Leeds â€¢Valerio Scarani, Centre for Quantum Technologies, NUS â€¢Philip Walther, University of Vienna â€¢Frances Wang, University of Illinois at Urbana-Champaign â€¢Wolfgang Wiltschko, University of Frankfurt
Title: Workshop on Quantum Cryptography with Finite Resources
Date/Time: 04-Dec, 12:00AM
Venue: Centre for Quantum Technologies, NUS
Workshop on Quantum Cryptography with Finite Resources (QCFR 2008) 4 - 6 December 2009 | Venue: Centre for Quantum Technologies, NUS (Singapore) Organised by: Valerio Scarani The workshop will bring together theorists and experimentalists involved in practical quantum cryptography. It aims at discussing how to derive security bounds for keys of finite length and to promote the implementations of these bounds in experiments, prototypes and commercial systems. List of confirmed participants â€¢Cyril Branciard (University of Geneva) â€¢Raymond Cai (Centre for Quantum Technologies) â€¢Philippe Grangier (Institut d'optique, Palaiseau) â€¢Masahito Hayashi (Tohoku University, Sendai) â€¢Thomas Jennewein (University of Vienna) â€¢Hermann Kampermann (University of Duesseldorf) â€¢Masato Koashi (Osaka University) â€¢Christian Kurtsiefer (Centre for Quantum Technologies) â€¢Anthony Leverrier (ENST Paris) â€¢Norbert Luetkenhaus (IQC Waterloo) â€¢Xiongfeng Ma (IQC Waterloo) â€¢Renato Renner (ETH Zurich) â€¢Valerio Scarani (Centre for Quantum Technologies) â€¢Yi Yang (USTC Hefei) â€¢Zhiliang Yuan (Toshiba, Cambridge) â€¢Anton Zavriev (MagiQ Technologies)
Title: Workshop on Quantum Algorithms and Complexity Theory
Date/Time: 17-Nov, 12:00AM
Venue: Centre for Quantum Technologies, NUS
Workshop on Quantum Algorithms and Complexity Theory 17 - 21 November 2008 | Venue: Physics Conference Room, S13 Level M, NUS (Singapore) Organised by: Miklos Santha, Andreas Winter and Rahul Jain The objective of this workshop is to give the opportunity to a few outstanding researchers to share their knowledge about the latest developments in the field of quantum algorithms and complexity theory. The Centre of Quantum Technologies at the campus of the National University of Singapore constitutes an ideal environment for both formal and informal scientific interactions. At the workshop there will be ample time for technical talks and for free discussions. Titles and Abstracts Workshop Programme Time Monday Tuesday Wednesday Thursday Friday 0900 Meet at the Hotel Main Lobby and transfer to NUS 0945 Ambainis Andris Ivanyos Gabor Massar Serge Buhrman Harry Keiji Matsumoto 1030 Kazuo Iwama Shparlinski, Igor Sen Pranab de Wolf Ronald Laplante Sophie 1115 Tea-break 1145 Lee Troy Hoyer Peter Wehner Stephanie Toner Ben Kerenidis Iordanis 1230 Lunch 1400 Singapore City Tour 1630 Reichardt Ben Raymond Rudy Magniez Frederic 1715 Spalek Robert Zhang Shengyu 1800 Technical Programme End 1900 Night Safari Tour Workshop Dinner List of confirmed participants â€¢Ambainis Andris, University of Latvia â€¢Buhrman Harry, CWI, Amsterdam â€¢HÃ¸yer Peter, University of Calgary â€¢Ivanyos GÃ¡bor, Informatics Laboratory , MTA, Budapest â€¢Iwama Kazuo, Kyoto University â€¢Keiji Matsumoto, National Institute of Informatics, Tokyo â€¢Kerenidis Iordanis, CNRS, UniversitÃ© Paris-Sud â€¢Klauck Hartmut, UniversitÃ¤t Frankfurt â€¢Lee Troy, Rutgers University â€¢Magniez FrÃ©dÃ©ric, CNRS, UniversitÃ© Paris-Sud â€¢Massar Serge, FNRS, UniversitÃ© Libre de Bruxelles â€¢Nayak Ashwin, University of Waterloo â€¢Raymond Rudy, Tokyo Research Lab., IBM Research â€¢Regev Oded, Tel-Aviv University â€¢Reichardt Ben, University of Waterloo â€¢Sen Pranab, TIFR, Mumbai â€¢Å palek Robert, Google, Mountain View â€¢Toner Ben, CWI, Amsterdam â€¢Wehner Stephanie, California Institute of Technology â€¢de Wolf Ronald, CWI, Amsterdam â€¢Zhang Shengyu, Chinese University, Hong Kong
Title: Mathematical Horizons for Quantum Physics
Date/Time: 28-Jul, 12:00AM
Venue: Institute for Mathematical Sciences, NUS
Overview Quantum theory is one of the most important intellectual developments in the early twentieth century. Since then there has been much interplay between theoretical physics and mathematics, both pure and applied. Arguably, the field of Mathematical Physics, equally at home in mathematics and in physics, emerged from John von Neumannâ€™s seminal work on the spectral theory of linear operators in Hilbert space which was triggered by the birth of quantum theory in the mid 1920s. Yet this is just one historical example of how the mathematical insights and tools that are developed in the course of answering challenging mathematical questions arising from physical problems have contributed to the advance of both mathematics and physics. In this tradition, it is the objective of this IMS Programme to bring together Mathematicians, whose work has a bearing on quantum physics, with researchers in Mathematical Physics and Theoretical Physics, whose work will benefit from the mathematical progress. The collaboration between these scientists of different background, different expertise, and different scientific culture will bear fruit on the research of all participants by intellectual cross-fertilization. In quantum physics, the observables are represented by (self-adjoint) linear operators on a Hilbert space, and states of the system are described as normalized positive linear functionals on an operator algebra. In the historically earliest stage, the spectrum of light emitted from atoms was explained by the spectral analysis of atomic Hamilton operators, and these investigations developed into the broad research field of Schrodinger operators. The modular theory of operator algebras brought about new contact points between mathematics and physics, which turned out to be beneficial for vast developments both in Mathematics and Theoretical Physics. Operator algebra theory became quite powerful and its applications in other branches of mathematics is described by the adjective â€œnon-commutative.â€ An example is probability theory, widely used in classical physics. The non-commutative probability theory is now well developed, typically called free probability theory, which has its earliest origin in Wignerâ€™s analysis of the spectrum of heavy atoms and is mathematically rooted in operator algebra theory. In summary, Operator Theory and Operator Algebra Theory form the mathematical basis of Quantum Physics and provide the indispensable mathematical language for theoretical studies in Quantum Physics. Not only are they used in Quantum Physics as powerful tools, but also they are often directly influenced by problems which arise in Quantum Physics. Thus, the unifying mathematical theme of the Programme is Non-Commutative Analysis. Activities The Programme will consist of four overlapping three-week Sessions, each devoted to a selected topic. In Session 1, the problem of bringing a given state to a target state by perturbing the interaction with a time-dependent external laser field is studied as a typical subject of quantum control. The specific form of problems in quantum control can stimulate a new development of non-commutative analysis in addition to solving physical problems. The random matrix, whose connection with quantum chaos is being studied, is a typical subject of non-commutative probability theory. (Note that probability theory and analysis are very closely related, especially free probability theory is based on operator algebra theory.) Session 2 is devoted to operator algebras in quantum information, which is a non- commutative analysis. Equilibrium statistical mechanics has been developed with full use of operator algebra theory, giving a strong influence backward. The same is expected of the subject of Session 3, which is non-equilibrium statistical mechanics. Session 4 deals with relativistic extensions of the traditional SchrÃ¶dinger operator theory when one is mainly concerned with atoms, molecules and solids on one hand, and deals with the operator algebra description of a system of infinitely many degrees of freedom when one is mainly concerned with the quantized radiation field. Both are cases of non-commutative analysis, mathematically speaking. Programme Structure Each Session has a Session Organizer who is in charge of defining the Session and the selection of the Discussion Leaders and the participants. At the start of each Session, there will be presentations by the Discussion Leaders to lay the groundwork. There follows an intense period of about 20 days of discussions and close collaborations among the participants. The Session ends with talks summarizing the progress accomplished and a round-table discussion defining future problems and areas of close collaboration. Overall Programme Coordinator: Prof. Huzihiro Araki (University of Kyoto) Session 1: Quantum Control and Dynamics â€¢Period: 28 Julyâ€“17 August 2008 (weeks 1-3) â€¢Organizer: Goong Chen (Texas A&M University) Topical Problems â€¢Molecular quantum control â—¦Discussion Leaders: Arne Keller (Universite Paris-Sud), and Hans-Rudolf Jauslin (UniversitÃ© de Bourgogne) â€¢Quantum chaos â—¦Discussion Leader: Stephan DeBievre (UFR de MathÃ©matiques et Laboratoire CNRS Paul PainlevÃ©) â€¢Laser-driven models in quantum computing systems â—¦Discussion Leader: Goong Chen (Texas A&M University) Report of Session 1: PDF Session 2: Operator Algebras in Quantum Information â€¢Period: 11â€“31 August 2008 (weeks 3-5) â€¢Organizers: Burkhard KÃ¼mmerer (Technische UniversitÃ¤t Darmstadt), Hans Maassen (Radboud University, Nijmegen) Topical Problems â€¢Entropy in quantum channels and the problem of additivity of quantum capacity â—¦Discussion Leader: Alexander Holevo (Steklov Mathematical Institute) â€¢Stability of quantum algorithms in the presence of external noise â—¦Discussion Leader: Mark Fannes (Katholieke Universiteit Leuven) â€¢Entanglement of multipartite and infinite systems â—¦Discussion Leader: Reinhard Werner (Technische UniversitÃ¤t Braunschweig Report of Session 2: PDF Session 3: Non-equilibrium Statistical Mechanics â€¢Period: 25 Augustâ€“14 September 2008 (weeks 5-7) â€¢Organizer: Claude Alain Pillet (UniversitÃ© du Sud Toulon-Var) Topical Problems â€¢Large deviation theory for quantum fluctuations â—¦Discussion Leader: Jan Derezinski (University of Warsaw) â€¢Non-equilibrium steady states â—¦Discussion Leader: Claude Alain Pillet (UniversitÃ© du Sud Toulon-Var) Report of Session 3: PDF Session 4: Strongly Interacting Many-Particle Systems â€¢Period: 1â€“21 September 2008 (weeks 6-8) â€¢Organizer: Heinz Siedentop (Ludwig-Maximilians-UniversitÃ¤t MÃ¼nchen) Topical Problems â€¢The theory of large atoms, molecules, and solids â—¦Discussion Leaders: Heinz Siedentop (Ludwig-Maximilians-UniversitÃ¤t MÃ¼nchen), Volker Bach (Johannes Gutenberg-UniversitÃ¤t Mainz) â€¢The mathematical description of the radiation field and its interaction with matter â—¦Discussion Leaders: Heinz Siedentop (Ludwig-Maximilians-UniversitÃ¤t MÃ¼nchen), Volker Bach (Johannes Gutenberg-UniversitÃ¤t Mainz) Report of Session 4 : PDF Public Lectures Title: Knot or not Knot? Date & Time: 13 Aug 2008, 6:30pm - 7:30pm Speaker: Burkhard KÃ¼mmerer, Technical University of Darmstadt, Germany Venue: LT31, Block S16, Science Drive 1, Singapore 117543 Title: Are Quantum Computers The Next Generation Of Supercomputers? Date & Time: 27 Aug 2008, 6:30pm - 7:30pm Speaker: Reinhard Werner, Technische UniversitÃ¤t Braunschweig, Germany Venue: LT31, Block S16, Science Drive 1, Singapore 117543 For attendance at these activities, please complete the online registration form. The following do not need to register: â€¢Invited speakers or participants. â€¢Those applying for membership with financial support. Membership Application The Institute for Mathematical Sciences invites applications for membership for participation in the above program. Limited funds to cover travel and living expenses are available to young scientists. Applications should be received at least three (3) months before the commencement of membership. Application form is available in (MSWord|PDF|PS) format for download. More information is available by writing to: Secretary Institute for Mathematical Sciences National University of Singapore 3 Prince George's Park Singapore 118402 Republic of Singapore or email to imssec(AT)nus.edu.sg. For enquiries on scientific aspects of the program, please email Jun Suzuki at physj(AT)nus.edu.sg. Program Coordinator â€¢Huzihiro Araki (Kyoto University) Organizing Committee Co-chairs â€¢Berthold Georg Englert (National University of Singapore) â€¢ Leong Chuan Kwek (Nanyang Technological University and National University of Singapore) Secretary â€¢Jun Suzuki (National Institute of Informatics, Japan) â€¢Bess Yiyuan Fang (National University of Singapore) Confirmed Visitors â€¢Overseas visitors â€¢Local visitors â€¢Graduate students â€¢ Registered local participants
Title: Demon Dynamics: Deterministic Chaos, the Szilard Map, and the Intelligence of Thermodynamic Systems
Date/Time: 13-Jan, 12:00AM
Venue: CQT Seminar Room, S15-03-15
Abstract: We introduce a deterministic chaotic systemâ€”the Szilard Mapâ€”that encapsulates the measurement, control, and erasure protocol by which Maxwellian Demons extract work from a heat reservoir. Implementing the Demon's control function in a dynamical embodiment, our construction symmetrizes Demon and thermodynamic system, allowing one to explore their functionality and recover the fundamental trade-off between the thermodynamic costs of dissipation due to measurement and due to erasure. The map's degree of chaosâ€”captured by the Kolmogorov-Sinai entropyâ€”is the rate of energy extraction from the heat bath. Moreover, an engine's statistical complexity quantifies the minimum necessary system memory for it to function. In this way, dynamical instability in the control protocol plays an essential and constructive role in intelligent thermodynamic systems.
Title: Holographic quantum error-correcting codes
Date/Time: 02-Feb, 12:00AM
Venue: CQT Seminar Room, S15-03-15
Abstract: In this talk, I will explore the recent connection between two profound ideas, quantum error correction and holography. The first, represents the realization that reliable quantum information processing could be achieved from imperfect physical components. The second, is a duality between two physical systems on different spatial dimensions which may be identified leading to the exact same predictions. Notably, only one of the two systems explicit includes gravitational features. Recently, quantum information has emerged as a natural tool to relate these two descriptions. As such, concepts familiar to quantum information scientists such as entanglement, compression and quantum error correction are playing important roles in understanding this duality. Conversely, the holographic duality is proposing a new lens through which to explore aspects of quantum error correction. In this talk, I will introduce some of the properties imposed by holography on corresponding quantum error-correcting codes, describe explicit tensor network codes which exhibit some of these properties and explore the implications of holographic predictions from a code-theoretic perspective.
Title: Secure quantum computation
Date/Time: 18-May, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: The realisation that conventional information theory and models of computation do not account for the full generality of states and operations described by quantum mechanics has led to the burgeoning field of quantum information processing. By harnessing quantum phenomena it is possible to produce stronger forms of cryptography and more efficient algorithms than could exist in a purely classical world. Computer security lies at the intersection of computation and cryptography, and has become an increasingly important topic in recent years. Since quantum information processing leads to advantages in cryptography and computation separately, it is natural to ask whether it may also enhance computer security. In this talk I will argue that the answer to this question is a resounding â€œyesâ€, and discuss recent developments in the field.
Title: Quantum simulations with strongly interacting photons: Merging condensed matter with quantum optics for quantum technologies
Date/Time: 27-Jul, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Classical computers require enormous computing power and memory to simulate even the most modest quantum systems. That makes it difficult to model, for example, why certain materials are insulators and others are conductors or even superconductors. R. Feynman had grasped this since the 1980s and suggested to use instead another more controllable and perhaps artificial quantum system as a "quantum computer" or specifically in this case a "quantum simulator". Working examples of quantum simulators today include extremely cold atoms trapped with lasers and magnetic fields and ions in electromagnetic traps. Photons and polaritons in light-matter systems have also recently emerged as a promising avenue especially for simulating out of equilibrium many-body phenomena in a natural driven-dissipative setting. I will briefly review in non-specialist terms the main results in this area including the early ideas on realizing Mott insulators, Fractional Hall states and Luttinger liquids with photons [1,2,3]. After that I will present in more detail a recent experiment in many-body localization physics using interacting photons in the latest superconducting quantum chip of Google [4]. A simple method to study the energy-levels-and their statistics - of many-body quantum systems as they go through the ergodic to many-body localized (MBL) transition, was proposed and implemented. The formation of a mobility edge of an energy band was observed and its shrinkage with disorder toward the center of the bands was measured, a direct observation of a canonical condensed matter concept perhaps for the first time. Beyond the applications in understanding fundamental physics, the potential impact of this field in different areas of quantum and nano technology and material science will be touched upon. References 1. D.G. Angelakis and C. Noh â€œMany-body physics and quantum simulations with lightâ€ Report of Progress in Physics, 80 016401 (2016) 2. "Quantum Simulations with Photons and Polaritons: Merging Quantum Optics with Condensed Matter Physics" edited by D.G. Angelakis, Quantum Science and Technology Series, Springer International Publishing, 2017, ISBN 978-3-319-52023-0, DOI 10.1007/978-3-319-52025-4 3. Keil, Noh, Rai, Stutzer, Nolte, Angelakis, A. Szameit "Optical simulation of charge conservation violation and Majorana dynamics", Optica 2, 454 (2015) 4. P. Roushan, C. Neill, J. Tangpanitanon,V.M. Bastidas,, â€¦, D.G. Angelakis, J. Martinis. â€œSpectral signatures of many-body localization of interacting photonsâ€, under review
Title: What do the data tell us?
Date/Time: 31-Aug, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: We gather information about physical systems by observation. In the realm of quantum physics, the experiments give us probabilistic data with natural statistical fluctuations that cannot be reduced by better instrumentation. What do such data tell us about the quantum system under study? A systematic and reliable answer can be given with the methods of quantum state estimation and quantum parameter estimation. I will report on recent developments.
Title: Evolution and Perspective of Planar Waveguide Devices
Date/Time: 07-Sep, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: The talk will review progress and future prospects of planar waveguide devices. Silica-based PLCs (planar lightwave circuits) and InP PICs (photonic integrated circuits) are widely used in the current WDM and FTTH systems. The success of silica PLCs and InP PICs strongly depends on their well controlled core geometries and refractive-index uniformities. On the other hand silicon photonics is widely regarded as a promising technology to meet the requirements of rapid bandwidth growth and energy-efficient communications while reducing cost per bit. One of the most prominent advantages of photonics interconnection over metallic interconnects is higher bandwidth and signal routing functionality using WDM technology. Expectations on Si photonics and technical challenges for silicon photonics will be described.
Title: Thermodynamics of Quantum Devices
Date/Time: 19-Oct, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Quantum thermodynamics addresses the emergence of thermodynamical laws from quantum mechanics. The viewpoint advocated is based on the intimate connection of quantum thermodynamics with the theory of open quantum systems. Quantum mechanics inserts dynamics into thermodynamics giving a sound foundation to finite-time-thermodynamics. The emergence of the 0-law I-law II-law and III-law of thermodynamics from quantum considerations will be presented through examples. I will show that the 3-level laser is equivalent to Carnot engine. I will reverse the engine and obtain a quantum refrigerator. Different models of quantum refrigerators and their optimization will be discussed. A heat-driven refrigerator (absorption refrigerator) is compared to a power-driven refrigerator related to laser cooling. This will lead to a dynamical version of the III-law of thermodynamics limiting the rate of cooling when the absolute zero is approached. The thermodynamically equivalence of quantum engines in the quantum limit of small action will be discussed. I will address the question why we find heat exchangers and flywheels in quantum engines. I will present a molecular model of a heat rectifier and a heat pump in a non-Markovian and strong coupling regime.
Title: Random words, longest increasing subsequences, and quantum PCA
Date/Time: 18-Feb, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Suppose you have access to i.i.d. samples from an unknown probability distribution $p = (p_1, â€¦, p_d)$ on $[d]$, and you want to learn or test something about it. For example, if you wants to estimate $p$ itself, then the empirical distribution will suffice when the number of samples, $n$, is $O(d/epsilon^2)$. In general, you can ask many more specific questions about $p$: Is it close to some known distribution $q$? Does it have high entropy? Etc. For many of these questions the optimal sample complexity has only been determined over the last $10$ years in the computer science literature. The natural quantum version of these problems involves being given samples of an unknown $d$-dimensional quantum mixed state $\rho$, which is a $d \times d$ PSD matrix with trace $1$. Many questions from learning and testing probability carry over naturally to this setting. In this talk, we will focus on the most basic of these questions: how many samples of $\rho$ are necessary to produce a good approximation of it? Our main result is an algorithm for learning $\rho$ with optimal sample complexity. Furthermore, in the case when $\rho$ is almost low-rank, we show how to perform PCA on it with optimal sample complexity. Surprisingly, we are able to reduce the analysis of our algorithm to questions dealing with the combinatorics of longest increasing subsequences (LISes) in random words. In particular, the main technical question we have to solve is this: given a random word $w \in [d]^n$, where each letter $w_i$ is drawn i.i.d. from some distribution $p$, what do we expect $\mathrm{LIS}(w)$ to be? Answering this question requires diversions into the RSK algorithm, representation theory of the symmetric group, the theory of symmetric polynomials, and many other interesting areas.
Title: Leibniz on Complexity
Date/Time: 10-Mar, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: 2016 is the tercentenary of the death of the remarkable philosopher/mathematician Leibniz. In this talk we shall present an appreciation of his work on information, computation and complexity leading up to modern work on algorithmic information and conceptual complexity, with applications in epistemological critiques of physics, mathematics and biology.
Title: Photonic Crystals and Photonic Molecules at Telcom Wavelengths
Date/Time: 30-Mar, 12:00PM
Venue: Photonic Crystals and Photonic Molecules at Telcom Wavelengths
Abstract: I will discuss the use of defects in photonic crystal waveguides to creates optical cavities which can control the emission of single quantum dots at telecom wavelengths. These waveguide structures enable complex geometries to be used in coupling two or more cavities together to produce photonic molecules. I will focus the talk on investigations of the mode splitting in a photonic molecule consisting of two coupled photonic crystal cavities separated by an optical well in a photonic crystal waveguide. Using a confocal microphotoluminescence mapping technique I will show that fine control of the coupling between the cavities can be achieved by the addition of an optical well. It is notable that an increase in the depth of the well results in an increased mode splitting and a strongly red shifted symmetric supermode (ground mode). Photonic molecules have recently been proposed for applications in cavity quantum electrodynamics (cQED) including the production of strong photon antibunching. These however require great control of the coupling strength between coupled cavities. We can finely tune the coupling between cavities embedded in a photonic crystal waveguide. Each cavity is formed by the local modulation of the waveguide width, which effectively defines two optical wells. A third narrower optical well is created by locally increasing the waveguide width between the cavities as shown by the red circles in figure (a). The coupled system studied here supports four supermodes as shown in figures (b)-(c).
Title: Shedding Starlight on the Quantum Fabric of Spacetime
Date/Time: 07-Apr, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Over the last decade there has been an intense effort using observations in astrophysics for setting constraints, with Planck-length sensitivity, on the properties of the laws of propagation of particles in a quantum spacetime. Importantly this has led to the demise of an old-fashioned naÃ¯ve assessment according to which Planck-scale effects could never be tested and research in quantum gravity should be confined to the realm of pure mathematics. I stress that the next few years might provide another formidable boost for this research area. For studies of systematic effects on particle propagation an exciting new window will result from "multimessenger analyses", combining information obtained with gamma rays, cosmological neutrinos and gravity waves. For studies of the effects of "fuzziness" (non-systematic quantum-spacetime effects) significant improvements are expected for searches of the associated decoherence effects.
Title: Fundamental tests of nature with cooled and stored exotic ions
Date/Time: 14-Apr, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: The presentation will concentrate on recent applications with exciting results of Penning traps in atomic and nuclear physics with cooled and stored exotic ions. These are high-accuracy mass measurements of short-lived radionuclides, g-factor determinations of the bound-electron in highly-charged, hydrogen-like ions and g-factor measurements of the proton and antiproton. The experiments are dedicated to nuclear-, neutrino- and astrophysics studies in the case of mass measurements on radionuclides, and to the determination of fundamental constants and a CPT test using g-factor measurements.
Title: Antihydrogen - a tool to study matter-antimatter symmetry in the laboratory
Date/Time: 22-Sep, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Antihydrogen, the bound state of an antiproton and a positron, is the simplest atom consisting purely of antimatter. Its matter counterpart, hydrogen, is one of the best studied atomic systems in physics. Thus comparing the spectra of hydrogen and antihydrogen offers some of the most sensitive tests of matter-antimatter symmetry. Furthermore, the availability of neutral antimatter offers for the first time a precise measurement of its gravitational interaction that was so far not possible due to the dominance of the electro-magnetic interaction for charged antiparticles. The formation and experimental investigation of antihydrogen is the main physics goal of several collaborations at the Antiproton Decelerator of CERN. The ASACUSA collaboration is pursuing a measurement of the ground-state hyperfine structure of antihydrogen in an atomic beam, a quantity which was measured in hydrogen using a maser to a relative precision of 10^{-12}. The AEgIS collaboration aims at using an ultra-cold beam of antihydrogen atoms and a classical moirÃ© deflectometer to determine the gravitational interaction between matter and antimatter in a first step to several percent precision. After a first production of cold antihydrogen in 2002 and a first trapping in 2010 the experiments are still in the process of optimising the antihydrogen production from trapped antiprotons and positrons. The status and prospect of these experiments will be reviewed.
Title: Magnetic imaging with point defects in diamond
Date/Time: 10-Nov, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: The ability to quantitatively map magnetic field distributions is of crucial importance for fundamental studies ranging from materials science to biology, and for the development of new devices e.g. in spintronics. Recently it has been demonstrated that scanning magnetometry based on a single spin associated to an impurities hosted in a solid is an efficient technique which combines high sensitivity and nanoscale resolution. The sensing signal relies on the optical detection of the electron spin resonance associated with a single nitrogen-vacancy (NV) center in diamond attached to a AFM tip. The magnitude of the stray magnetic field above a magnetic sample can then be determined from the Zeeman shifts of the energy levels associated to this artificial atom in the solid state. Extending this technique to a cryogenic environment will open the way to investigate many magnetic phenomena occuring in complex condensed matter systems, such as superconductivity or the magnetic properties of strongly correlated systems. I will present our recent realizations of a scanning magnetometer based on NV centers in a nanodiamond grafted at the apex of a AFM tip, and how they have been applied to the imaging of magnetic nanostructures. I will also describe how NV centers can be efficiently engineered by combining plasma-assisted diamond growth and nanoscale ion implantation.
Title: Exploring quantum matter with photons
Date/Time: 17-Nov, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: From the beginning of the 20th century, photons have provided a paradigm for the crucial effects of quantum mechanics. In this century, advances in quantum devices have led the way to strong photon-photon interactions, merging the best coherence properties of light with many-body physics. I will discuss our efforts for realizing nontrivial phases of matter using optical- and microwave-domain photons. While our ability to control the single-particle properties of light via photonic crystal and metamaterial techniques provides a useful tool kit for single-particle physics, going to the many-body regime has crucial challenges to be overcome. I will emphasize how we can overcome these difficulties, by developing strong nonlinearities with light, creating a chemical potential for photons, and extending these ideas into other gauge theories.
Title: The Quantum Approximate Optimization Algorithm: A Good Choice to Run on a Near Term Quantum Computer
Date/Time: 07-Dec, 04:30PM
Venue: Auditorium 1 Level 1, Town Plaza University Town, NUS
Abstract: I will describe a quantum algorithm for approximate optimization and explain how to analyze its performance on all instances of particular combinatorial optimization problems. I will explain why this algorithm is well suited to run on small scale quantum computers because of its low circuit depth and simple gate structure. I will also explain how, in principle, running this algorithm can demonstrate Quantum Supremacy because if a classical algorithm could efficiently sample its output then the Polynomial Hierarchy would collapse.
Title: From quantum philosophy to quantum technology
Date/Time: 07-Dec, 06:00PM
Venue: Auditorium 1 Level 1, Town Plaza University Town, NUS
Abstract: Quantum physics has become one of the best confirmed scientific theories ever devised by mankind and it is firmly embedded in many modern technologies. The fact that quantum concepts often seem to contradict traditional notions of reality, space, time or logic has inspired fundamental philosophical debates as well as even further intriguing developments in quantum computing, communication, simulation, sensing and metrology. Based on a tutorial review of the state of the art in the field, we will focus on the concept of matter-waves, which was originally put forward by Louis de Broglie in 1923 â€œto solve almost all the problems brought up by quantaâ€, and cast in mathematical form by Erwin SchrÃ¶dinger in 1926. We will see how modern matter-wave interferometry can serve in sophisticated tests of fundamental physics and as a subtle force sensor with many interdisciplinary applications.
Title: Dipole QED: an alternative paradigm for quantum non-linear optics and non-equilbrium dynamics
Date/Time: 16-Apr, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: In cavity QED (cQED), mirrors alter the electromagnetic field in the vicinity of an emitter and thereby modify the light-matter interaction in a significant way. In the strong coupling regime, the effect of the cavity dominates over the coupling to the vacuum. Similarly in dipole QED (dQED), one or more dipoles in the vicinity of the emitter modifies both the vacuum coupling (sub- or super-radiance) and the resonant frequency. The condition for strong coupling is simply that the dipoles must be closer than the reduced wavelength of emission, which is of order tens of nanometers for optical emitters [1] or millimeters for microwave emitters, e.g. transitions between highly-excited Rydberg states in atoms [2]. We will discuss experiments in both these regimes [1,2] and then discuss applications of dQED in single photon non-linear optics [3,4], and non-equilbrium systems with long-range interactions [5].
Title: A single charge in a Bose-Einstein condensate: from two to few to many-body physics
Date/Time: 28-May, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Electrons attract polarizable atoms via a 1/r^4 potential. For slow electrons the scattering from that potential is purely s-wave and can be described by a Fermi pseudopotential. To study this interaction Rydberg electrons are well suited as they are slow and trapped by the charged nucleus. In the environment of a high pressure discharge Amaldi and Segre, already in 1934 observed a lineshift proportional to the scattering length [1]. At ultracold temperatures and Rydberg states with medium size principle quantum numbers n, one or two ground state atoms can be trapped in the meanfield potential created by the Rydberg electron, leading to so called ultra-long range Rydberg molecules [2]. At higher Rydberg states the spatial extent of the Rydberg electron orbit is increasing. For principal quantum numbers n in the range of 100-200 and typical BEC densities, up to several ten thousand ground state atoms are located inside one Rydberg atom, We excite a single Rydberg electron in the BEC, the orbital size of which becomes comparable to the size of the BEC. We study the coupling between the electron and phonons in the BEC [3]. We also observe evidence for ultracold collisions involving a single ion which is shielded by a Rydberg electron. Reactive processes due to few-body Langevin dynamics are mostly l-changing and lead to molecule formation. As an outlook, the trapping of a full condensate inside a Rydberg atom of high principal quantum number, the imaging of the Rydberg electron's wave function by its impact onto the surrounding ultracold cloud as well as the observation of polaron formation seem to be within reach [4]. [1] E. Amaldi and E. Segre, Nature 133, 141 (1934) [2] C. H. Greene, et al., PRL 85, 2458 (2000); V. Bendkowsky et al., Nature 458, 1005 (2009) [3] J . B. Balewski, et al., Nature 502, 664 (2013) [4] T. Karpiuk, et al., arXiv:1402.6875
Title: Black Holes, Firewalls, and the Complexity of States and Unitary Transformations
Date/Time: 20-Aug, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: I'll discuss some recent results, motivated by the black-hole firewall paradox and the AdS/CFT correspondence, about the quantum circuit complexity of preparing certain entangled states and implementing certain unitary transformations. One result is a strengthening of an argument by Harlow and Hayden: I'll show that, under plausible assumptions, "decoding" useful information from Hawking radiation, as called for by the AMPS "firewall" thought experiment, requires the computational power to invert arbitrary cryptographic one-way functions, something we think not even quantum computers could do in sub-astronomical time. A second result, joint with Lenny Susskind, considers the circuit complexity of the kinds of states that could arise in AdS/CFT, and shows that, under a reasonable conjecture about complexity classes (PSPACE is not in PP/poly), the complexity indeed becomes superpolynomially large, as predicted by a conjectured relationship between complexity and geometry. I'll also discuss more general problems about the complexities of states and unitary transformations, which I find fascinating even apart from the quantum-gravity motivation.
Title: Certified Quantum Randomness
Date/Time: 07-Dec, 04:30PM
Venue: University Hall Auditorium Level 2, Lee Kong Chian Wing University Hall, NUS
Abstract: Randomness is a physical phenomena which we are confronted with all the time. Will it rain today? At what time? Will the train be on time? But are such phenomena truly random? Good randomness is essential for many applications. Cryptography, the art of hiding information from malicious users, is only as good as the source of randomness that underlies it. Quantum mechanics, the theory of microscopic phenomena, can only predict the probability of events: for instance quantum theory can only predict the probability that a radioactive nucleus will decay, not if the nucleus will decay. Does this mean that microscopic phenomena are truly random? By studying systems of two entangled particles, it can be shown both theoretically and experimentally, that events at the microscopic scale are truly random, truly unpredictable. Beyond its philosophical implications, these works also have important potential applications. Indeed they imply that one can build random number generators that certify that they work correctly. That is, if the random number generator malfunctions in some way, if the numbers it produces cease to be random, this will automatically be detected. By extending this idea, one could also build quantum cryptographic systems and quantum computers that certify that they work correctly. We discuss the perspectives for practical implementations.
Title: Computing beyond the Age of Mooreâ€™s Law
Date/Time: 07-Dec, 06:00PM
Venue: University Hall Auditorium Level 2, Lee Kong Chian Wing University Hall, NUS
Abstract: With the end of Mooreâ€™s Law within sight (really!), what opportunities exist to continue the exponential scaling of computer performance and efficiency into the future? The primary consumers of energy and time in computers today are not the processors, but rather the communication and storage systems in a data center. Even if it were possible to perform computation infinitely fast with zero energy consumption, there would be little change in the power and time required to perform a calculation on the types of â€˜big dataâ€™ sets that are beginning to dominate information technology. I will describe a path forward with two stages. The first is to change the fundamental structure of a computer from the processor-centric von Neumann paradigm that has dominated for the past seven decades to a memory-driven architecture based on a flat nonvolatile memory space, high bandwidth photonic interconnect and dispersed system-on-chip processors. This is the vision behind The Machine, a major research and development effort currently in progress in Hewlett Packard Enterprise. Once this transformation has been completed, a new era of hybrid computation can begin, which is the motivation behind a new Nanotechnology-Inspired Grand Challenge for Future Computing recently announced by the US White House. One of the drivers for this initiative is the thesis that although our present understanding of the brain is limited, we know enough now to design and build circuits that can accelerate certain computational tasks; and as we learn more about how brains communicate and process information, we will be able to harness that understanding to create a new exponential growth path for computing technology.
Title: Cats, Decoherence and Quantum Measurement
Date/Time: 27-Feb, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: In this talk it is our intention to review the basic ideas of how entanglement relates to the so-called SchrÃ¶dinger cat state and present a paradigmatic situation where states very similar to that one can be created. The example we have chosen is the SQUID ring which depending on the external bias allows us to implement a wealth of interesting physical situations to be treated. We shall argue that in these situations the question of dissipation is really relevant and the concept of decoherence naturally arises. Once we have accomplished that we discuss some possible implications of decoherence to the quantum theory of measurement . As a matter of fact, we shall employ an alternative measure of quantum correlation which goes beyond entanglement â€“ the quantum discord â€“ with the same purpose. We finally present recent experimental results performed with twin photons which corroborate our predictions. This Colloquium is jointly organised with Graphene Research Centre, NUS
Title: Non-quantum Entanglement and Bell Violation Analogs
Date/Time: 13-Mar, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: We are interested in non-quantum entanglement in the context of probabilistic classical theories. We will examine a category of correlation measurements in statistical optics prompted by the following remark of John Bell: "It can indeed be shown that that the quantum mechanical correlations cannot be reproduced by a hidden variables theory even if one allows a 'local' sort of indeterminism. ... This would not work."
Title: Quantum Photonics: Perspectives and challenges
Date/Time: 03-Jul, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: I will review the status of quantum photonics focussing on the recent developments in spontaneous four wave mixing (FWM) in optical fibre1,2 and in silicon waveguides3. I will show that 4-photon and 6-photon experiments are now achievable with fibre sources but also that the scalability is primarily limited by loss. This is illustrated by recent 6-N00N interferometry demonstrations4 and a variety of cluster state based experiments5. In all experiments to date quantum advantage can be inferred within a detection post-selected sub-set of photons but this detection rate drops exponentially with increasing photon number. The integration of all components onto one chip could bring very large photon number experiments closer if waveguide, switching and detector losses can be made small. A future roadmap to making scalable quantum processors with linear optics resources is beginning to form but will require significant resource overhead. I will comment on emerging alternatives to linear optics approaches based on one dimensional cavities and waveguides that could reduce this overhead significantly6. [1] McMillan,et al Narrowband high-fidelity all-fibre source of heralded single photons at 1570 nm, Opt. Express 17, 6156-6165 (2009). [2] Halder, et al, Nonclassical 2-photon interference with separate intrinsically narrowband fibre sources, Opt. Express 17, 4670-4676 (2009). [3] Silverstone, et al, On-chip quantum interference between two silicon waveguide sources, Nature Photonics 8, 104 (2014). [4] Bell, et al, Multi-Colour Quantum Metrology with Entangled Photons, Phys. Rev. Letts. 111, 093603 (2013). [5] Bell, et al, Experimental characterization of universal one-way quantum computing, New J. Phys. 15, 053030 (2013). [6] Young et al, Polarization engineering in photonic crystal waveguides for spin-photon entanglers, arXiv 1406.0714
Title: A Mixture of Fermi and Bose Superfluids
Date/Time: 19-Aug, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Superconductivity and superfluidity are spectacular macroscopic manifestations of genuine quantum collective effects with, today, vast domains of applications. In this family of quantum solids or fluids, ultracold gases and polaritons are the last born. Thanks to the great flexibility of laser cooling and trapping methods, ultracold gases offer to study these quantum correlated systems with a new twist. It is possible for instance to tune the strength and sign of the interaction between atoms. Optical lattices, realized by interfering laser beams, create periodic optical potentials that mimic the crystalline potential seen by electrons in solids. In liquid helium and dilute gases, Bose and Fermi superfluidity has been observed separately, but producing a mixture where both the fermionic and the bosonic components are superfluid has been challenging. In this talk, we will describe the production of such a mixture of Bose and Fermi superfluids with dilute gases of two Lithium isotopes, 6Li and 7Li [1]. The mixture is remarkably stable and we probe the collective dynamics of this system by exciting center-of-mass oscillations that exhibit extremely low damping below a certain critical velocity. Using high precision spectroscopy of these modes we observe coherent energy exchange and measure the coupling between the two superfluids. Our observations can be captured theoretically using a sum-rule approach that we interpret in terms of two coupled oscillators. Tuning the attractive interaction in the Fermi superfluid, we measure the two speeds of sound in the mixture in the crossover between BEC of deeply bound dimers and BCS superfluidity. This provides a new method to probe the equation of state of the Fermi superfluid. [1] I. Ferrier-Barbut, M. Delehaye, S. Laurent, A. Grier, M. Pierce, B. Rem, F. Chevy, C. Salomon, ArXiv :1404.2548
Title: A single ion in a Penning Trap: Test of QED and a new value for the electronÂ´s mass
Date/Time: 04-Sep, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: The magnetic moment of the electron bound in hydrogen-like ions has been measured with high precision. We perform Zeeman-spectroscopy using single ions confined in a triple-Penning trap. The results are compared with QED calculations and represent to date the most precise QED test in bound systems. From a comparison of theory and experiment in C5+ where QED contributions are small and well known, we derive a value for the electronÂ´s atomic mass which is more than one order of magnitude more precise than previously known. References: S. Sturm et al., g Factor of Hydrogen-like 28Si13+, Phys. Rev. Lett. 107, 023002 (2011) S. Sturm et a,, High precision measurement of the atomic mass of the electron, Nature 506, 467 (2014)
Title: Matter and Light: sharing ideas and concepts in the quantum world
Date/Time: 15-Oct, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: With the development of quantum engineering, the traditionally separated fields of condensed matter physics and quantum optics are exchanging ideas and concepts to their mutual benefit. In the first part of the talk, I will recap the development of electronic structure theory in materials from weak- to strong interactions and then discuss how ideas on strong correlations have penetrated into cold atomic physics and cavity optics in the last decade. In the second part I will discuss a reverse example, how ideas on entanglement, typically a realm of quantum optics, have started to penetrate into mesoscopic physics and define the new field of electronic optics.
Title: Quantum coherence in photosynthetic proteins: insights for emerging energy technologies
Date/Time: 28-Jul, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Coherence beating has been observed in two dimensional optical spectroscopy of several photosynthetic proteins ranging from light harvesting antennae isolated from algae, plant and bacteria to photosynthetic reaction centres isolated from plants. For the majority of these complexes the leading hypothesis for the physical mechanism supporting coherence beating is an intertwined electronic and vibrational dynamics whereby a single quanta of energy is quasi-coherently shared between these degrees of freedom. Does this mechanism lead to a similar or different picture for the energetics in these biological complexes? In this lecture I will discuss our research efforts towards addressing this question and the lessons we may learn for emerging bio-inspired energy technologies.
Title: Quantum information and the monogamy of entanglement
Date/Time: 08-Dec, 04:00PM
Venue: Ngee Ann Kongsi Auditorium Level 2 Education Resource Centre University Town, NUS
Abstract: The recent field of quantum information and computing approaches quantum mechanics not as a source of paradoxes or difficulties, but as a new theory of information. For example, Heisenberg's uncertainty principle can be seen not only as limitation on our ability to measure, but also can be used to construct new methods of sending secret messages. In this talk, I will first give an overview of the mathematics of quantum information and computing. Then I'll discuss a phenomenon known as "monogamy of entanglement" that has been a recent focus of my own research. Entanglement is a quantum analogue to correlations from probability theory. Unlike correlations, however, entanglement cannot be shared without limit; i.e. it is monogamous. I will discuss the surprising implications of this fact for mathematics, physics and computer science.
Title: The Quantum Way of Doing Computations
Date/Time: 08-Dec, 05:00PM
Venue: Ngee Ann Kongsi Auditorium Level 2 Education Resource Centre University Town, NUS
Abstract: Since the mid nineties of the 20th century it became apparent that one of the centuriesâ€™ most important technological inventions, computers in general and many of their applications could possibly be further enormously enhanced by using operations based on quantum physics. This is timely since the classical roadmaps for the development of computational devices, commonly known as Mooreâ€™s law, will cease to be applicable within the next decade due to the ever smaller sizes of the electronic components that soon will enter the quantum physics realm. Computations, whether they happen in our heads or with any computational device, always rely on real physical processes, which are data input, data representation in a memory, data manipulation using algorithms and finally, the data output. Building a quantum computer then requires the implementation of quantum bits (qubits) as storage sites for quantum information, quantum registers and quantum gates for data handling and processing and the development of quantum algorithms. In this talk, the basic functional principle of a quantum computer will be reviewed. It will be shown how strings of trapped ions can be used to build a quantum information processor and how basic computations can be performed using quantum techniques. In particular, the quantum way of doing computations will be illustrated by analog and digital quantum simulations and the basic scheme for quantum error correction will be introduced and discussed. Scaling-up the ion-trap quantum computer can be achieved with interfaces for ion-photon entanglement based on high-finesse optical cavities and cavity-QED protocols, which will be exemplified by recent experimental results.
Title: Random for whom?
Date/Time: 08-Dec, 06:00PM
Venue: Ngee Ann Kongsi Auditorium Level 2 Education Resource Centre University Town, NUS
Abstract: There is a difference between the impossibility of predicting the weather and the impossibility of giving a value to both position and momentum of an electron. This difference is what makes quantum physics hard to understand: intrinsic randomness. In this talk, I shall try to clarify what "intrinsic randomness" means, how we can be sure that it is "real" and not an artefact of an imperfect theory. Besides shaping our view of the natural world in an unexpected way, the existence of intrinsic randomness may even lead to practical benefits
Title: A high-energy particle experiment on a tabletop: what you can learn at 100 meV that you can't learn at 100 TeV
Date/Time: 23-Jan, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Any time anyone has ever measured, the north and south poles of an electron are seen to be identical. But there are good theoretical reasons to suspect that upon closer examination we may find a discrepancy. Observing such a discrepancy would be the equivalent recording a spark chamber track of a never before seen supersymmetric particle. We will take advantage of nature's high-electric-field laboratory -- a polar molecule -- to reach new levels of sensitivity to the electon's hypothetical electric dipole moment.
Title: New Lattice Gauge Theories From Quantum Computation
Date/Time: 21-Mar, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: I present some views and perspectives on the notions of Fault-Tolerant Quantum Computation with topological codes Next, I present current results on how the process of external quantum error correction on topological color codes (TCCs) leads to new versions of LGTs (Lattice Gauge Theories). In particular, we find that: i/ A complete study of error correction in TCCs yields the error threshold of p_c = 4.5(2)%. ii/ A novel Abelian lattice gauge theory with gauge group Z_2xZ_2 and a peculiar lattice and gauge structure that departs from the standard formulations of Wegner and Wilson. We refer to it as a tricolored LGT. Its structure reflects the error history in color codes, rather than the discretization of a continuous gauge theory. iii/ A novel approach to pinpoint first-order phase transitions in LGTs with disorder using the skewness of the average over Wilson loop operators. Finally, we show how to increase the error threshold up to 18.9(3)% when noise correlations are taken into account in depolarizing channels
Title: Information thermodynamics and fluctuation theorems
Date/Time: 04-Apr, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: The second law of thermodynamics presupposes a clear-cut distinction between the controllable and uncontrollable degrees of freedom by means of macroscopic operations. The cutting-edge technologies in quantum information and nanoscience seem to require us to abondon such a working hypothesis in favor of the distinction between the accessible and inaccessible degrees of freedom. In this talk, I will talk about the fundamentals of such information thermodynamics together with the related new results on fluctuation theorems
Title: Quantum Computation of Prime Number Functions
Date/Time: 16-May, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: We propose a quantum circuit that creates a pure state corresponding to the quantum superposition of prime numbers. This {\em Prime} state can be built using an oracle which is a quantum implementation of the classical Miller-Rabin primality test. The {\em Prime} state is highly entangled, and its entanglement measures encode number theoretical functions such as the distribution of twin primes or the Chebyshev bias. This algorithm can be further combined with the quantum Fourier transform to yield an estimate of the prime counting function, more efficiently than any classical algorithm and with an error below the bound that allows for the verification of the Riemann hypothesis. Arithmetic properties of prime numbers are then, in principle, amenable to experimental verifications on quantum systems.
Title: Quoins Versus Coins
Date/Time: 18-Jul, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Human monkeys are used to thinking about the problem of choosing from a set of objects according to some desired, biased, probability distribution. Just think about how you chose your partner(s). Even when it is easy for you to do such a sampling (eg Monte Carlo sampling is sometimes easy in condensed matter physics), it can be difficult to do a quantum sampling (Q-Sampling) of the same distribution. By Q-Sampling I mean the creation of a coherent superposition of states of such objects whose amplitudes are the (square roots of) of the specified distribution. In this talk I will discuss what we do know about this problem, why it is interesting, and will discuss how it can let us achieve tasks with quantum information that are provably impossible classically. Unlike most (if not all) other such tasks in quantum information, this one does not have to do with communication per se.
Title: Energy Fluctuations and Maxwell Demon in Nano-electronic Circuits
Date/Time: 25-Jul, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: In small systems, such as molecules or nanostructures, energy fluctuations play an important role, and the second law of thermodynamics, for example, applies only on the average. The distribution of entropy production and the work performed under non-equilibrium conditions are then governed by so-called fluctuation relations [1 - 3]. I apply these concepts to a single-electron box [4,5], and present an experimental demonstration of fluctuation relations in them [6,7]. Single-electron circuits provide furthermore a basic example of a Maxwell Demon, where information can be converted into energy [8]; here the information is collected by a detector with single-electron sensitivity. Finally I discuss the subtle issues of work and heat in open quantum systems. I use superconducting qubits as examples of driven systems in this context [9,10]. [1] C. Jarzynski, Nonequilibrium equality for free energy differences, Phys. Rev. Lett. 78, 2690 (1997). [2] G. E. Crooks, Entropy production fluctuation theorem and the nonequilibrium work relation for free energy differences, Phys. Rev. E 60, 2721 (1999). [3] U. Seifert, Entropy Production along a Stochastic Trajectory and an Integral Fluctuation Theorem, Phys. Rev. Lett. 95, 040602 (2005). [4] D.V. Averin and J.P. Pekola, Statistics of the dissipated energy in driven single-electron transitions, EPL 96, 67004 (2011). [5] J. P. Pekola and O.-P. Saira, Work, Free Energy and Dissipation in Voltage Driven Single-Electron Transitions, J. Low Temp. Phys. 169, 70 (2012). [6] O.-P. Saira, Y. Yoon, T. Tanttu, M. MÃ¶ttÃ¶nen, D. V. Averin, and J. P. Pekola, Test of Jarzynski and Crooks fluctuation relations in an electronic system, Phys. Rev. Lett. 109, 180601 (2012). [7] J. V. Koski et al., Distribution of entropy production in nonequilibrium single-electron tunneling, arXiv:1303.6405. [8] D. V. Averin, M. MÃ¶ttÃ¶nen, and J. P. Pekola, Maxwell's demon based on a single-electron pump, Phys. Rev. B 84, 245448 (2011). [9] J. P. Pekola, P. Solinas, A. Shnirman, and D. V. Averin, Calorimetric measurement of quantum work, arXiv:1212.5808 (2012). [10] F. W. J. Hekking and J. P. Pekola, Quantum jump approach for work and dissipation in a two-level system, arXiv:1305.5207.
Title: Superoscillations and weak measurement
Date/Time: 03-Oct, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Band-limited functions can oscillate arbitrarily faster than their fastest Fourier component over arbitrarily long intervals. Where such â€˜superoscillationsâ€™occur, functions are exponentially weak. In typical monochromatic optical fields, substantial fractions of the domain (one-third in two dimensions) are superoscillatory. Superoscillations have implications for signal processing, and raise the possibility of sub-wavelength resolution microscopy without evanescent waves. In quantum mechanics, superoscillations correspond to weak measurements, suggesting â€˜weak valuesâ€™ of observables (e.g photon momenta) far outside the range represented in the quantum state. A weak measurement of neutrino speed could lead to a superluminal result without violating causality, but the effect is too small to explain the speed claimed in a recent experminent.
Title: Uncertainty Principle and Quantum Reality
Date/Time: 28-Nov, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Abstract: In this talk, I will review my proposal to reformulate Heisenberg's uncertainty principle [1-3] and its recent experimental confirmation [6]. The new formulation allows us simultaneous measurements of totally non-commuting observables [4]. We will discuss how this affects our understanding of quantum reality along the line with a recent mathematical reconstruction of Bohr's reply to Einstein-Podolsky-Rosen on their paradox [5]. References. [1] M. Ozawa, Universally valid reformulation of the Heisenberg uncertainty principle on noise and disturbance in measurement, Phys. Rev. A 67, 042105/1-042105/6 (2003). [2] M. Ozawa, Uncertainty principle for quantum instruments and computing, Int. J. Quant. Inf. 1, 569--588 (2003). [3] M. Ozawa, Uncertainty relations for noise and disturbance in generalized quantum measurements, Ann. Phys. (N.Y.) 311, 350-416 (2004). [4] M. Ozawa, Quantum reality and measurement: A quantum logical approach, Found. Phys. 41, 592-607 (2011). [5] M. Ozawa and Y. Kitajima, Reconstructing Bohr's Reply to EPR in Algebraic Quantum Theory, Found. Phys. 42, 475-487 (2012). [6] J. Erhart, S. Sponar, G. Sulyok, G. Badurek, M. Ozawa, and Y. Hasegawa, Experimental demonstration of a universally valid error-disturbance uncertainty relation in spin-measurements, Nature Phys. 8, 185-189 (2012).
Title: Superconducting Circuits for Quantum Information Processing: How Electric Circuits Behave Quantum Mechanically
Date/Time: 06-Dec, 04:00PM
Venue: Ngee Ann Auditorium, Asian Civilisations Museum, 1 Empress Place, Singapore 179555
Abstract: We all benefit from the amazing technologies of silicon large-scale integrated circuits (Si LSI) in our mobile phones, tablets, PCs, etc. It is almost incredible that billions of nanometer-scale transistors in a processor operate synchronously with a nanosecond clock cycle. Indeed, the emergence of the silicon empire in the last century is one of the biggest achievements of quantum mechanics and solid-state physics based on it. Nevertheless, circuit engineers are never bothered with quantum mechanics: While the dynamics of individual electrons can only be understood in the quantum languages, the operations of the devices are described fully classically, i.e., either ON or OFF. In contrast, superconducting circuits with a proper design can behave quantum mechanically in a macroscopic scale: Superposition of ON and OFF states is allowed in the quantum bit devices. I will discuss how to integrate such quantum bits and how to control and measure the quantum states toward realizing a superconducting quantum information processor.
Title: Simulating Quantum Behaviour with Quantum Computers
Date/Time: 06-Dec, 05:00PM
Venue: Ngee Ann Auditorium, Asian Civilisations Museum, 1 Empress Place, Singapore 179555
Abstract: In 1982, Richard Feynman proposed the concept of a quantum computer as a means of simulating physical systems that evolve according to the SchrÃ¶dinger equation. Since that time, a rich theory of quantum computing has developed, which includes quantum algorithms for simulating physical systems (as well as for several other computing problems). I will explain various quantum algorithms that have been proposed for Feynman's simulation problem, including my recent work (jointly with Dominic Berry and Rolando Somma) that dramatically improves the running time as a function of the precision of the output data.
Title: Make It Small and Take It Outside!
Date/Time: 06-Dec, 06:00PM
Venue: Ngee Ann Auditorium, Asian Civilisations Museum, 1 Empress Place, Singapore 179555
Abstract: Quantum physics allows us to model the behavior of matter and energy at the atomic and molecular level (and even beyond!) with a very high precision. Unfortunately, the devices needed to control and observe these quantum effects are often large and unwieldy, making the deployment of quantum-inspired technology a serious challenge. At the Centre for Quantum Technologies there is a program called the Small Photon-Entangling Quantum System that seeks to build and deploy complete entangled photon generators/detectors that have a small physical footprint. These devices are designed to operate autonomously in remote nodes of quantum communication networks. An example would be nanosatellites in low earth orbit. I will present the key design parameters that have enabled us to reduce the resource requirements and will discuss the outlook for experiments and applications.
Title: Quantum Theory of the Classical
Date/Time: 12-Jan, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: I discuss three insights into the transition from quantum to classical. I will start with (i) a minimalist (decoherence-free) derivation of preferred states. Such pointer states define events (e.g., measurement outcomes) without appealing to Born's rule. Probabilities and (ii) Bornâ€™s rule can be derived from the symmetries of entangled quantum states. With probabilities at hand one can analyze information flows from the system to the environment in course of decoherence. They explain how (iii) robust â€œclassical realityâ€ arises from the quantum substrate by accounting for objective existence of pointer states of quantum systems through redundancy of their records in the environment. Taken together, and in the right order, these three advances elucidate quantum origins of the classical.* *W. H. Zurek, Nature Physics 5, 181-188 (2009).
Title: Experimental Quantum Error Correction
Date/Time: 12-Jan, 05:30PM
Venue: CQT Seminar Room, S15-03-15
Abstract: The Achilles' heel of quantum information processors is the fragility of quantum states and processes. Without a method to control imperfection and imprecision of quantum devices, the probability that a quantum computation succeed will decrease exponentially in the number of gates it requires. In the last fifteen years, building on the discovery of quantum error correction, accuracy threshold theorems were proved showing that error can be controlled using a reasonable amount of resources as long as the error rate is smaller than a certain threshold. We thus have a scalable theory describing how to control quantum systems. I will briefly review some of the assumptions of the accuracy threshold theorems and comment on recent experiments that have been done and should be done to turn quantum error correction into an experimental reality.
Title: Carbon Spintronics
Date/Time: 09-Feb, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Carbon, in the form of graphene and carbon nanotubes, has recently emerged as an interesting alternative material for electronics. Here, we argue that carbon is also a unique material for a new type of electronics that is based on the electron spin rather than its charge, known as spintronics, and in particular for spin-based quantum computing [1]. Due to the low concentration of nuclear spins and relatively weak spin-orbit coupling, carbon-based structures allow for long coherence times, which is the primary figure of merit for the quality of a spin quantum bit (qubit). We discuss the formation of quantum dots, acting as electron â€œtrapsâ€™â€™, in graphene and their potential use for quantum information processing. In diamond, the spin coherence of defect centers can persist even at ambient temperatures. After introducing this fascinating quantum system, we briefly present a particular mechanism for storing and retrieving quantum information in an atomic nucleus in diamond [2]. [1] B. Trauzettel, D. Bulaev, D. Loss, and G. Burkard, Nature Phys. 3, 192 (2007). [2] G. D. Fuchs, G. Burkard, P. V. Klimov, and D. D. Awschalom, Nature Phys. 7, 789 (2011).
Title: Breaking the bounds of quantum thermodynamics
Date/Time: 08-Mar, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: I shall revisit the traditional formulation of the three laws of thermodynamics and the bounds they imply on thermodynamic observables , and argue that all of these have to be modified and reformulated when the system is enacted upon on time scales shorter than the bath memory time. Practical consequences related to work extraction and cooling will be demonstrated to be in stark contrast with existing schemes .
Title: Simulating quantum transport with atoms and light
Date/Time: 24-May, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: The transport of quantum particles in non ideal material media (eg the conduction of electrons in an imperfect crystal) is strongly affected by scattering from impurities of the medium. Even for a weak disorder, semi-classical theories, such as those based on the Boltzmann equation for matter-waves scattering from the impurities, often fail to describe transport properties and full quantum approaches are necessary. The properties of the quantum systems are of fundamental interest as they show intriguing and non-intuitive phenomena that are not yet fully understood such as Anderson localization, percolation, disorder-driven quantum phase transitions and the corresponding Bose-glass or spin-glass phases. Understanding quantum transport in amorphous solids is one of the main issues in this context, related to electric and thermal conductivities. Ultracold atomic gases can now be considered to revisit the problem of quantum conductivity and quantum transport under unique control possibilities. Dilute atomic Bose-Einstein condensates (BEC) and degenerate Fermi gases (DFG) are produced routinely taking advantage of the recent progress in cooling and trapping of neutral atoms. Transport has been widely investigated in controlled potentials with no defects, for instance periodic potentials (optical lattices). Controlled disordered potentials can also be produced with various techniques such as the use of magnetic traps designed on atomic chips with rough wires, the use of localized impurity atoms, the use of radio-frequency fields or the use of optical potentials. This recently lead to the observation of the Anderson Localization of a BEC in 1D and 3D,and the study of diffusion properties during matter-wave transport.
Title: Doing small systems: Fluctuation relations and the arrow of time
Date/Time: 26-Jul, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: This talk is aimed at highlighting issues that relate of doing thermodynamics and statistical physics of finite size systems. This theme gained considerable importance in view of fascinating advances in nanotechnology and system biology. While the fathers of thermodynamics developed the famous 5 Laws of Thermodynamics (incl. a â€œâ€“1_Law), having in mind macroscopic systems, these grand concepts need to be inspected anew in view of the fact that the fluctuations grow with decreasing size to a level where they even may play the dominant role. This holds true particularly for the inter-relationships between fluctuations and, importantly, the measurements of work, heat & heat flow and thermodynamic equilibrium quantifiers such as (non-fluctuating) free energy changes or production of thermodynamic entropy. -- Subtleties occur in equilibrium thermodynamics for small systems, such as the role of finite size for quantities like (possibly negative-valued) canonical heat capacitance in presence of strong system-environment coupling. I further elaborate on recent, timely results for nonequilibrium classical and quantum fluctuation relations. An attempt is made to outline pitfalls and still open issues (relativistic and others) together with those inherent difficulties that likely do emerge with the experimental validation scenarios of such relations. Finally, a connection between Fluctuation Relations, nonlinear Response and its feasible relation with the ever-lasting intriguing challenge in detecting the origin of an "Arrow of Time" will be elucidated. This presentation is based on joint work with Michele Campisi, Gert-Ludwig Ingold and Peter Talkner, all at the University of Augsburg. -- Own pertinent recent works that apply for the theme of this talk are: [1] G. L. Ingold, P. HÃ¤nggi, and P. Talkner Specific heat anomalies of open quantum systems Phys. Rev. E 79, 061105 (2009) [2] M. Campisi, P. Hanggi, and P. Talkner Colloquium: Quantum fluctuation relations: Foundations and applications Rev. Mod. Phys. 83, 771--791 (2011); Addendum and Erratum: Quantum fluctuation relations: Foundations and applications Rev. Mod. Phys. 83, 1653 (2011). [3] M. Campisi and P. Hanggi Fluctuation, Dissipation and the Arrow of Time Entropy 13, 2024--2035 (2012).
Title: The evasive cheshire cat: How to detect fractional statistics
Date/Time: 02-Aug, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Certain strongly correlated electronic systems give rise to quantized low energy excitations which possess fractional statistics. A number of protocols to detect such quasi particlesâ€”anyons-- have been proposed in recent years, yet the quest for fractional statistics has not resulted in an unequivocal manifestation. I will review some of theoretical proposals for detection of anyons, and discuss why it is so difficult to find them
Title: Generating and exploiting intense attosecond pulses
Date/Time: 06-Sep, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: During the last decade we have systematically developed methods and instrumentation leading to the coherent emission of intense XUV pulses of sub-femtosecond duration. As a measure of the term "intense" we identify the feasibility in inducing observable non-linear processes solely by the XUV radiation. Non-linear XUV processes are essential in (a) attosecond pulse metrology, (b) XUV-pump-XUV-probe studies of ultrafast dynamics, (c) reaching highest spatiotemporal resolution and d) exploring new physics in inner-shell non-linear or even strong field processes. We regard the above as current and future main steam developments in attoscience. I will review the physics and technology behind intense attosecond pulse train [1,2] and coherent XUV supercontinuum [3] generation, as well as recent XUV-pump-XUV-probe studies at the boundary between fempto- and atto-second scales [4]. 1.P. Tzallas, D. Charalambidis, N.A. Papadogiannis, K. Witte and G. D. Tsakiris Nature 426, 267 (2003) 2.Y. Nomura, R. HÃ¶rlein, P. Tzallas, B. Dromey, S. Rykovanov, S. Major, J. Osterhoff, S. Karsch, M. Zepf, D. Charalambidis, F. Krausz, G.D. Tsakiris Nature Physics 5, 124 (2009) 3.P. Tzallas, E. Skantzakis, C. Kalpouzos, E. Benis, G. D. Tsakiris and D. Charalambidis Nature Physics 3, 846 (2007) 4.P. Tzallas, E. Skantzakis, L. A. A. Nikolopoulos, G. D. Tsakiris and D. Charalambidis Nature Physics 7, 781 (2011)
Title: Single-atom spin qubits in silicon
Date/Time: 25-Oct, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: The idea of using the spin of a single donor atom in silicon to encode quantum information goes back to the Kane proposal [1] in 1998. The proposal was motivated by two observations: (i) Silicon is one of the most promising materials to host spin qubits in solid state, owing to the very weak spin-orbit coupling, and to the possibility to eliminate decoherence from nuclear spins by isotopic purification; (ii) A trillion-dollar worth industry already exists, that has developed extraordinary tools to manufacture silicon nanoscale devices in a reliable and cost-effective way. The proposal appeared ambitious, visionary but very challenging at the time, because it relied upon the non-trivial assumption that the progress in the fabrication of classical silicon devices could be harnessed to pursue quantum information goals. Indeed, over a decade of intense efforts has been necessary before the first breakthroughs in silicon quantum technologies could be demonstrated. I will present the first experimental demonstration of a qubit based on a single phosphorus atom in silicon. The atom is coupled to a silicon Single-Electron Transistor, and the whole device is fabricated retaining standard CMOS technologies such as ion implantation [2] and metal gates fabricated on top of high-quality silicon oxide [3]. In a single-atom device, we have demonstrated single-shot readout [4] and coherent control [5] of the donor electron spin, as well and the spins of the 31P nucleus and of a strongly-coupled 29Si nucleus. All three qubits exhibit excellent coherence and high-fidelity readability, with the nuclear ones being accessible through a quantum nondemolition measurement. These results represent major milestones in the search for a scalable and coherent quantum computer platform, and confirm the vision of silicon as the choice material for both quantum and classical technologies. [1] B. E. Kane, Nature 393, 133 (1998). [2] D. N. Jamieson et al., Appl. Phys. Lett. 86, 202101 (2005). [3] A. Morello et al., Phys. Rev. B 80, 081307(R) (2009). [4] A. Morello et al., Nature 467, 687 (2010). [5] J. J. Pla et al., Nature (2012), in press.
Title: Fluctuoscopy of Superconductors and Dynamics of Abrikosovâ€™s Lattice Formation Close to Hc2(0)
Date/Time: 29-Nov, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: I start my lecture from qualitative discussion, based on the Heisenberg principle, of the nature of thermal fluctuations in superconductor at temperatures above the critical one. Then the analogous consideration is applied to the regime of quantum fluctuations at zero temperature above the field Hc2(0). Basing both on microscopic and qualitative analysis we demonstrate, that here, fluctuating Cooper pairs rotating in magnetic field present themselves precursor images of Abrikosovâ€™s vortices and form the clusters with specific superconducting features. I evaluate both the characteristic size QF( H) and lifetime QF( H) of such formations. When magnetic field reaches Hc2(0) from above the size and lifetime of such clusters tend infinity and the order, corresponding Abrikosovâ€™s lattice is established. In second part of the lecture I discuss fluctuoscopy - the method of investigation of intrinsic properties of superconductors by means of the detailed analysis of their fluctuation magneto-conductivity, tunneling characteristics, Nernst coefficient throughout the phase diagram.
Title: Randomness
Date/Time: 07-Dec, 04:00PM
Venue: NUS Kent Ridge, University Hall Auditorium, Level 2, Lee Kong Chian Wing
Abstract: Is the universe inherently deterministic or probabilistic? Perhaps more importantly - can we tell the difference between the two? Humanity has pondered the meaning and utility of randomness for millennia. There is a remarkable variety of ways in which we utilize perfect coin tosses to our advantage: in statistics, cryptography, game theory, algorithms, gamblingâ€¦ Indeed, randomness seems indispensable! Which of these applications survive if the universe had no randomness in it at all? Which of them survive if only poor quality randomness is available, e.g. that arises from "unpredictable" phenomena like the weather or the stock market? A computational theory of randomness, developed in the past three decades, reveals (perhaps counter-intuitively) that very little is lost in such deterministic or weakly random worlds. In the talk I'll explain the main ideas and results of this theory.
Title: Quantum Technology for a Networked World
Date/Time: 07-Dec, 06:00PM
Venue: NUS Kent Ridge, University Hall Auditorium, Level 2, Lee Kong Chian Wing
Abstract: The 21st Century has seen the emergence of a networked world, connected by global fibre-optic communications and mobile phones, with geo-location provided through GPS, and all this has changed our lives more dramatically than at any time since the industrial revolution. Quantum-enabled technology is at the heart of this change. I will describe how communications depend on lasers that are shot noise limited, geo-located and synchronized by atomic clocks that depend on atomic coherence. New developments in quantum technology, and in particular miniature atomic clocks that utilize concepts such as coherent population trapping have the potential for even more dramatic applications. Some of these include comms systems immune to GPS jamming (of real importance for global security), as well as quantum sensors for medical applications (including cardiography, neurophysiology, etc), sensitive magnetometry, gyros, and geophysical surveying. I will describe the basic quantum phenomena being exploited as well as prospects for exploitation.
Title: Controlling and Exploring Quantum Gases at the Single Atom Level
Date/Time: 07-Dec, 04:00PM
Venue: NUS University Hall Auditorium, Lee Kong Chian Wing, Level 2
Title: An atomic superfluid Bose-Einstein condensate in a ring
Date/Time: 07-Nov, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: We create an atomic-gas Bose-Einstein condensate in a ring-shaped trap and interrupt the circulation in the ring with a repulsive barrier. This system can exhibit behavior similar to that of a superconducting loop interrupted by a weak link or Josephson junction. We observe controllable, discrete phase slips (jumps in the phase winding number around the ring) and hysteretic behavior in such a system. A novel interference measurement can detect the presence, direction, and winding number of the circulation in the ring as well as provide a determination of the current-phase relationship of the weak link.
Title: Probabilities Versus Amplitudes
Date/Time: 07-Dec, 06:00PM
Venue: NUS University Hall Auditorium, Lee Kong Chian Wing, Level 2
Title: Quantum flows in polariton condensates
Date/Time: 24-Nov, 12:00AM
Venue: CQT Seminar Room, S15-03-15
Abstract: Superfluidity, the ability of a quantum fluid to flow without friction, is one of the most spectacular phenomena occurring in degenerate gases of interacting bosons. Since its first discovery in liquid helium-4, superfluidity has been observed in quite different systems, and recent experiments with ultra-cold trapped atoms have explored the subtle links between superfluidity and Boseâ€“Einstein condensation. In semiconductor microcavities, exciton-polaritons, which are mixed light-matter quasi-particles arising from the strong coupling between photons and excitons, have been shown to form Bose-Einstein condensates. It has been predicted that polaritons should behave as a novel quantum fluid, with unique properties stemming from their intrinsically non-equilibrium nature and their very low mass (~10-4 times that of the electron, inherited from their photonic component). This has stimulated the quest for an experimental demonstration of superfluidity effects in polariton systems. I will present our recent results, demonstrating superfluid motion of polaritons, which manifests itself as the suppression of scattering from defects when the flow velocity is slower than the speed of sound in the fluid. Cerenkov-like wake patterns, vortices and dark solitons are also observed when the flow velocity is varied. The experimental findings are in quantitative agreement with predictions based on a generalized Grossâ€“Pitaevskii theory, and establish microcavity polaritons as a system for exploring the rich physics of non-equilibrium quantum fluids.
Title: Quantum Information Processing and Chemistry
Date/Time: 06-Oct, 12:00AM
Venue: CQT Seminar Room, S15-03-15
Abstract: In this talk, I overview some of the aspects that intersect quantum information science and problems in chemistry. In particular, I will describe the simulation of chemical dynamics and electronic structure using quantum computers, both algorithms and experimental implementations. I will discuss the use of quantum adiabatic or annealing devices for solving lattice heteropolymer models associated with protein folding.
Title: Spinor- and Rydberg- Polaritons
Date/Time: 11-Aug, 12:00AM
Venue: CQT Seminar Room, S15-03-15
Abstract: Slow-light polaritons are quasi-particles generated in the interaction of light with multi-level atoms driven by an external laser close to a Raman resonance. Their dispersion relation can be controlled to a large extend, representing massive Schroedinger particles on the one hand or multi-component, i.e. spinor objects with a Dirac-like spectrum on the other. In the latter case "relativistic" length and energy scales can be widely tuned, making relativistic effects accessible in the lab. Making use of the tunability of the mass the delocalization transition of the random-mass Dirac model with off-diagonal disorder can be experimentally observed. In the second part of the talk the prospects to create strong interactions between dark-state polaritons using Rydberg atoms will be discussed. The dipole-dipole coupling between atoms in a Rydberg state leads to a strong and long-range interaction between polaritons, as well as to a blockade phenomenon. This interacion can give rize to interesting many-body phenomena, such as two-particle correlations which are much stronger than possible for pointlike interacting particles, crystallization of photons or quantum Hall states.
Title: Anderson Localization â€“ looking forward.
Date/Time: 28-Jul, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Localization of the eigenfunctions of quantum particles in a random potential was discovered by P.W. Anderson more than 50 years ago. In spite of its respectable maturity and intensive theoretical and experimental studies this field is far from being exhausted. Anderson localization was originally discovered in connection with spin relaxation and charge transport in disordered conductors. Later this phenomenon was observed for light, microwaves, sound, and more recently for cold atoms. Moreover, it became clear that the domain of applicability of the concept of localization is much broader. For example, it provides an adequate framework for discussing the transition between integrable and chaotic behavior in quantum systems. We will discuss current understanding of the Anderson localization and its manifestation in different physical situations. We will illustrate the main idea by several examples from adiabatic quantum computation to many-body statistical mechanics. We will demonstrate that physics of disordered many-body quantum systems can be described in the framework of the Anderson Localization.
Title: Is smell a quantum sense ?
Date/Time: 26-May, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Our sense of smell is a extraordinarily good at molecular recognition: we can identify tens of thousands of odorants unerringly over a wide concentration range. The mechanism by which this happens do so is still hotly debated. One view is that molecular shape governs smell, but this notion has turned out to have very little predictive power. Some years ago I revived a discredited theory that posits instead that the nose is a vibrational spectroscope, and proposed a possible underlying mechanism, inelastic electron tunneling. In my talk I will review the history and salient facts of this problem and describe some recent experiments that go some way towards settling the question.
Title: Dipole-Dipole Interactions in the Frozen Rydberg Gas
Date/Time: 24-Mar, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Experiments probing the dipole-dipole interactions in a frozen Rydberg gas made from 300Î¼K Rb in a magneto optical trap are described. Resonant energy transfer measurements, in which the energy of an initial pair of atoms is tuned into resonance with the energy of a final state pair exhibit widths in excess of the simplest binary interaction estimates. We attribute the larger than expected widths to the existence of many body interactions and the fact that since the detection favors close pairs of atoms. In contrast, recent measurements of the dipole-dipole broadening of ns-np microwave transitions show less broadening than the simplest estimates and cusped lineshapes. These observations can be understood by considering several factors; the reduction, even to zero, of the dipole-dipole energy shifts due to the spin-orbit interaction, the strengths of the allowed microwave transitions, and the fact that many of the atoms are in low density regions of the trap. While the gas is frozen on a 1Î¼s time scale, the attractive force associated with the dipole-dipole interaction leads to ionizing collisions on a 5-10 Î¼s time scale, which can in turn lead to the spontaneous evolution to a plasma. There are, however, open questions related to the evolution to a plasma.
Title: Integrated Quantum Photonics
Date/Time: 10-Feb, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Quantum information science aims to harness uniquely quantum mechanical properties to enhance measurement and information technologies, and to explore fundamental aspects of quantum physics. Of the various approaches to quantum computing [1], photons are particularly appealing for their low-noise properties and ease of manipulation at the single qubit level [2]. Encoding quantum information in photons is also an appealing approach to quantum communication, metrology (eg. [3]), measurement (eg. [4]) and other quantum technologies [5]. However, the implementation of optical quantum circuits with bulk optics has reached practical limits. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturisation and scalability [6]. Here we report high-fidelity silica-on-silicon integrated optical realisations of key quantum photonic circuits, including two-photon quantum interference and a controlled-NOT logic gate [7]. We have demonstrated controlled manipulation of up to four photons on-chip, including high-fidelity single qubit operations, using a lithographically patterned resistive phase shifter [8]. We have used this architecture to implement a small-scale compiled version of Shor's quantum factoring algorithm [9] and demonstrated heralded generation of tuneable four photon entangled states from a six photon input [10]. We have combined waveguide photonic circuits with superconducting single photon detectors [11]. We describe complex quantum interference behaviour in multi-mode interference devices with up to eight inputs and outputs [12], and quantum walks of correlated particles in arrays of coupled waveguides [13]. Finally, we give an overview of our recent work on fundamental aspects of quantum measurement [14,15] and single photon sources [16,17]. [1] T. D. Ladd, F. Jelezko, R. Laflamme, Y. Nakamura, C. Monroe, and J. L. OBrien, Nature 464, 45 (2010). [2] J. L. O'Brien, Science 318, 1567 (2007). [3] T. Nagata, R. Okamoto, J. L. O'Brien, K. Sasaki, and S. Takeuchi, Science 316, 726 (2007). [4] R. Okamoto, J. L. O'Brien, H. F. Hofmann, T. Nagata, K. Sasaki, and S. Takeuchi, Science 323, 483 (2009). [5] J.L.O'Brien, A.Furusawa, and J.Vuckovic, Nature Photon. 3, 687 (2009). [6] A. Politi, M. J. Cryan, J. G. Rarity, S. Yu, and J. L. O'Brien, Science 320, 646 (2008). [7] A. Laing, A. Peruzzo, A. Politi, M. R. Verde, M. Halder, T. C. Ralph, M. G. Thompson, and J. L. O'Brien, Appl. Phys. Lett. 97, 211109 (2010) [8] J. C. F. Matthews, A. Politi, A. Stefanov, and J. L. O'Brien, Nature Photon. 3, 346 (2009). [9] A. Politi, J. C. F. Matthews, and J. L. O'Brien, Science 325, 1221 (2009). [10] J. C. F. Matthews, A. Peruzzo, D. Bonneau, and J. L. O'Brien, arXiv:1005.5119 [11] C. M. Natarajan, A. Peruzzo, S. Miki, M. Sasaki, Z. Wang, B. Baek, S. Nam, R. H. Hadfield, and J. L. O'Brien, Appl. Phys. Lett. 96, 211101 (2010). [12] A. Peruzzo, A. Laing, A. Politi, T. Rudolph, and J. L. O'Brien, Nature Comm. in press; arXiv:1005.5119 [13] A. Peruzzo, M. Lobino, J. C. F. Matthews, N. Matsuda, A. Politi, K. Poulios, X.-Q. Zhou, Y. Lahini, N. Ismail, K. Worhoff, Y. Bromberg, Y. Silberberg, M. G. Thompson, and J. L. O'Brien, Science 329, 1500 (2009) [14] A. Laing, T. Rudolph, and J. L. O'Brien, Phys. Rev. Lett. 102, 160502 (2009). [15] X-Q Zhou, TC Ralph, P Kalasuwan, M Zhang, A Peruzzo, BP Lanyon, and JL OBrien arXiv:1006.2670 [16] J. P. Hadden, J. P. Harrison, A. C. Stanley-Clarke, L. Marseglia, Y.-L. D. Ho, B. R. Patton, J. L. OBrien, and J. G. Rarity, Appl. Phys. Lett. 97, 241901 (2010) [17] C. Xiong, G. D. Marshall, A. Peruzzo, M. Lobino, A. S. Clark, D.-Y. Choi, S. J. Madden, C. M. Natarajan, M. G. Tanner, R. H. Hadfield, S. N. Dorenbos, T. Zijlstra, V. Zwiller, M. G. Thompson, J. G. Rarity, M. J. Steel, B. Luther-Davies, B. J. Eggleton, J. L. Oâ€™Brien arXiv:1011.1688
Title: Random numbers certified by Bellâ€™s Theorem
Date/Time: 09-Feb, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Randomness is an intriguing concept which has fascinated, and keeps fascinating, many different communities, from Philosophy to Physics and Mathematics. On the other hand, randomness has also become a useful resource, as random numbers are used, for instance, in cryptographic applications, gambling or the simulation of physical and biological systems. Up to now, any of the existing solutions for randomness generation had to face the following problems: (i) certification: how can one prove that the obtained symbols are truly random? (ii) privacy: how can one be sure that the generated symbols are also random to any other external observer and (iii) device-independence: how do imperfections in the devices used in the generation process affect the randomness of the generated symbols? We provide a novel formalism for randomness generation which solves all these problems: using the non-local correlations of entangled quantum states, it is possible to generate certifiable, private and device-independent randomness.
Title: Information is Quantum: How physics has helped us understand what information is and what can be done with it.
Date/Time: 11-Jan, 05:00PM
Venue: Ngee Ann Kongsi Auditorium (Level 2), Singapore Management University
Abstract: The information revolution is largely based on what a physicist would call a classical view of information, assuming that it can be copied freely and is not disturbed by observation. Quantum effects in information processing, which prevent the information in microscopic objects like atoms or photons from being observed or copied accurately, were long regarded as a mere nuisance, but are now known to make possible feats such as quantum cryptography, quantum teleportation and dramatic computational speedups. Although progress toward a practical quantum computer is slow, other surprising quantum informational effects continue to be discovered, and quantum cryptographic systems are already available commercially. Most importantly, the quantum approach has led to a more coherent and powerful way of thinking about how physical objects interact and influence one another, and how that interaction can be used to compute, communicate, and protect privacy. This talk will avoid mathematical complications and instead aim to explain central quantum concepts like entanglement, which at first sight seem counterintuitive.
Title: CQT Annual Symposium - The Famous, The Bit and The Quantum
Date/Time: 07-Dec, 12:00AM
Venue: NUS University Hall Auditorium, Lee Kong Chian Wing, Level 2
Title: Where is Quantum Mechanics Likely to Break Down?
Date/Time: 09-Sep, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Quantum theory is very robust and nobody knows where it will break down. However, there are certain structural weaknesses that offer clues as to where it may ultimately falter. One is its total disconnect to gravity at a very fundamental level (a physical level, not due to mathematical problems like non-linearity, etc). Even at the level of the equivalency principle there is a basic incompatibility, which can be traced back to the lack of a fundamental length scale (independent of the Planck length, which is important but not relevant here). We believe such a scale exists and will be ultimately responsible for the breakdown of the theory as we know it today.
Title: Quantum-limited measurements: One physicist's crooked path from quantum optics to quantum information
Date/Time: 20-Aug, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: We will first review the recent progress in atomic clocks operating in the microwave and optical domain of the electromagnetic spectrum. The second of the SI system of units is realized today with an accuracy of 3 10-16 by a number of laser cooled atomic fountains worldwide. Optical clocks have recently reached a frequency stability and accuracy in the 10-18 range [1] opening new perspectives for time keeping and fundamental tests. We will then present the status of the ACES mission of the European Space Agency scheduled for flight to the International Space Station from 2013 to 2015 [2]. ACES will embark a laser cooled cesium clock designed for microgravity operation (PHARAO ), an active hydrogen maser (SHM), and a high precision time transfer system operating in the microwave domain. This microwave link (MWL) will enable frequency comparisons between the space clocks and a network of ground based clocks belonging to worldwide metrology institutes and universities. The link is designed for obtaining a relative frequency resolution of 10-17 after a few days of measurement duration for intercontinental comparisons. In 2009-2010, all elements of the flight payload have successfully passed the Engineering Model tests and flight models are under construction. We will present the latest measurement results and flight model designs. In a second part we will describe tests of fundamental physical laws using ultra-stable clocks in space and on the ground that are planned for the ACES mission. An improved measurement of Einstein's gravitational red-shift will be made at the two parts per million level. By comparing clocks of different nature at the 10-17/year level, new limits will be obtained for the time variation of the fundamental constants of physics such as the fine structure constant alpha and the ratio of electron to proton mass. The ability to compare microwave and optical clocks using the recently developed frequency comb technique opens a wide range of possibilities in clock comparisons. Finally a new kind of relativistic geodesy based on the Einstein effect will provide information on the Earth geoid, complementing the recent determination obtained by space geodesy methods. References: [1]C. W. Chou, D. B. Hume, J. C. J. Koelemeij, D. J. Wineland, and T. Rosenband, Phys. Rev. Lett. 104, 070802 (2010) [2] L. Cacciapuotti, and C. Salomon, Eur. Phys. J. Special Topics, 172, 57 (2009)
Title: Space Clocks and Fundamental Tests
Date/Time: 10-Aug, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: We will first review the recent progress in atomic clocks operating in the microwave and optical domain of the electromagnetic spectrum. The second of the SI system of units is realized today with an accuracy of 3 10-16 by a number of laser cooled atomic fountains worldwide. Optical clocks have recently reached a frequency stability and accuracy in the 10-18 range [1] opening new perspectives for time keeping and fundamental tests. We will then present the status of the ACES mission of the European Space Agency scheduled for flight to the International Space Station from 2013 to 2015 [2]. ACES will embark a laser cooled cesium clock designed for microgravity operation (PHARAO ), an active hydrogen maser (SHM), and a high precision time transfer system operating in the microwave domain. This microwave link (MWL) will enable frequency comparisons between the space clocks and a network of ground based clocks belonging to worldwide metrology institutes and universities. The link is designed for obtaining a relative frequency resolution of 10-17 after a few days of measurement duration for intercontinental comparisons. In 2009-2010, all elements of the flight payload have successfully passed the Engineering Model tests and flight models are under construction. We will present the latest measurement results and flight model designs. In a second part we will describe tests of fundamental physical laws using ultra-stable clocks in space and on the ground that are planned for the ACES mission. An improved measurement of Einstein's gravitational red-shift will be made at the two parts per million level. By comparing clocks of different nature at the 10-17/year level, new limits will be obtained for the time variation of the fundamental constants of physics such as the fine structure constant alpha and the ratio of electron to proton mass. The ability to compare microwave and optical clocks using the recently developed frequency comb technique opens a wide range of possibilities in clock comparisons. Finally a new kind of relativistic geodesy based on the Einstein effect will provide information on the Earth geoid, complementing the recent determination obtained by space geodesy methods. References: [1]C. W. Chou, D. B. Hume, J. C. J. Koelemeij, D. J. Wineland, and T. Rosenband, Phys. Rev. Lett. 104, 070802 (2010) [2] L. Cacciapuotti, and C. Salomon, Eur. Phys. J. Special Topics, 172, 57 (2009)
Title: Computing with Quantum Knots: Majorana Fermions, Non-Abelian Anyons, and Topological Quantum Computation
Date/Time: 27-May, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: I will discuss the revolutionary new concept of topological quantum computation, which is fault-tolerant at the hardware level with no need, in principle, of any quantum error correction protocols. Errors simply do not happen since the physical qubits and the computation steps are protected against decoherence by non-local topological correlations in the underlying physical system. The key idea is non-Abelian statistics of the quasiparticles (called 'anyons' as opposed to fermions or bosons), where the space-time braiding of the anyons around each other, i.e. quantum 'knots', form topologically protected quantum gate operations. I will describe in details the status of the subject by discussing the theoretical principles guiding the experimental search for the appropriate topological phases of matter where such non-Abelian anyons may exist. Among the most significant possibilities are certain even-denominator fractional quantum Hall states, exotic chiral p-wavesuperconductors, sandwich structures made from superconductors/semiconductors or superconductors/insulators, and suitable cold atomic systems. In the context, I will also discuss the race to find Majorana fermions in solid state systems, with the Majorana fermions being the simplest generic examples of non-Abelian objects in nature. I will explain how the subject of topological quantum computation synergistically brings together conformal field theory and advanced mathematics on one hand with materials science and quantum information on the other
Title: Quantum Optics in Wavelength Scale Structures
Date/Time: 22-Apr, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: The interaction between light and matter in optical structures that are at or below the wavelength scale could provide unprecedented performance in the storage of data, the switching of light and the generation of light of tailored properties. For instance wavelength scale confinement can enhance non-linear effects. An example is our experiments on four wave mixing effects in micron diameter optical fibres which provide novel sources of entangled photon pairs. Also by creating nanoscale light traps, cavities, in wavelength scale periodic dielectric structures we can drastically modify light emission from 'atom like' objects (quantum dots, colour centres). In the case of long light-storage times we can achieve strong coupling which is a form of entanglement between the atom-cavity system and single photons. When we couple light in and out of these structures we will see strong non-linear effects down to the single photon level. Thus we could make a low power switch at light levels orders of magnitude below existing technology. We can also expect to exploit the quantum properties as ultimately we have the single photon non-linear element needed for quantum computation. I will show a few example results to illustrate these ideas and discuss future plans now funded through an ERC advanced grant.
Title: One World Versus Many
Date/Time: 18-Mar, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: There is a compelling intellectual case for exploring whether purely unitary quantum theory defines a sensible and scientifically adequate theory, as Everett originally proposed. Many different and incompatible attempts to define a coherent Everettian quantum theory have been made over the past fifty years, suggesting this is a problem about which humans are excellent at forming strong intuitions but very bad at forming persuasive arguments. In this talk I review recent work in this area. I argue that considerable light is shed on the problem once one realizes that many-worlds theories are just that -- novel and distinct scientific theories, not reinterpretations of standard quantum theory. This forces us to reconsider from first principles whether (and if so how) we can relate many-worlds theories to empirical data. I review some interesting and ingenious attempts in this direction by Wallace, Greaves-Myrvold and others, and explain why they don't work.
Title: Quantum optics with Rydberg atoms
Date/Time: 26-Oct, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: There have been growing research activities involving Rydberg atoms in different directions of quantum optics, both fundamental and applied. In this talk, I first briefly review a few systems and examples, which exploit the exotic properties of Rydberg atoms for new phenomena and applications. I then discuss some of our experimental efforts, including electromagnetically induced transparency and microwave-optical conversion using Rydberg atoms.
Title: Magic Square, Quantum Mathematics, and Computing Theory
Date/Time: 08-Dec, 04:00PM
Venue: NUS Kent Ridge, University Hall Auditorium, Level 2, Lee Kong Chian Wing
Title: Sculpting a spinor condensate: from Skyrmions to quantum memory
Date/Time: 19-Nov, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: The spin and orbital angular momentum of a spinor Bose-Einstein condensate can be controlled using optical fields that carry orbital angular momentum. I will describe how this process works and our experimental progress using this approach to manipulate the BEC wavefunction. In particular, I will describe the creation of complex spin textures, coreless vortices and Skyrmions. I will also describe the application of this work to the realization of a robust memory for quantum information processing.
Title: Exploring Flatland with cold atoms
Date/Time: 29-Oct, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: In his world-famous novel "Flatland" published in 1884, the English writer Edwin Abbott imagined a social life in a two-dimensional world. With a very original use of geometrical notions, E. Abbott produced a unique satire of his own society. Long after Abbott's visionary allegory, Microscopic Physics has provided a practical path for the exploration of low-dimensional worlds. With the realization of quantum wells for example, it has been possible to produce two-dimensional gases of electrons. The properties of these fluids dramatically differ from the standard three-dimensional case, and some of them are still lacking a full understanding. During the last decade, a novel environment has been developed for the study of low-dimensional phenomena. It consists of cold atomic gases that are confined in tailor-made electromagnetic traps. With these gases, one hopes to simulate and understand more complex condensed-matter systems. The talk will discuss some aspects of this research, both from an experimental and a theoretical perspective. Connections with other domains of many-body physics, such as the Quantum Hall phenomenon, will also be addressed.
Title: Coherence and control of single electron spins in quantum dots
Date/Time: 03-Sep, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Individual electron spins isolated in semiconductor quantum dots are natural two-level quantum systems that could form the basis of a quantum information processor. Using a fully electrical approach, it is now possible to initialize, coherently manipulate and read out the spin state of a single electron in a quantum dot, and to couple it coherently to the spin of an electron in a neighbouring dot. Furthermore, we have come to a quantitative understanding of the timescales and mechanisms by which the spin loses phase coherence. Ongoing work focuses on integrating all buildings blocks in a single experiment, and on either control or elimination of the electron spin environment, in particular the nuclear spins in the quantum dot host material. This should permit using entangled spins as a new resource for quantum information processing. References R. Hanson, L.P Kouwenhoven, J.R. Petta, S. Tarucha, and L.M.K. Vandersypen, Spins in few-electron quantum dots, Reviews of Modern Physics 79, 1217 (2007) I. T.Vink, K. C. Nowack, F. H. L. Koppens, J. Danon, Yu. V. Nazarov, and L. M. K. Vandersypen, Locking electron spins into magnetic resonance by electron-nuclear feedback, arXiv:0902.2659 F.H.L. Koppens, K.C. Nowack, and L.M.K. Vandersypen, Spin echo of a single electron spin in a quantum dot, Phys. Rev. Lett. 100, 236802 (2008) K.C. Nowack, F.H.L. Koppens, Yu.V. Nazarov and L.M.K. Vandersypen, Coherent control of a single electron spin with electric fields, Science 318, 1430 (2007) F.H.L. Koppens, C. Buizert, K.J. Tielrooij, I.T. Vink, K.C. Nowack, T. Meunier, L.P. Kouwenhoven, and L.M.K. Vandersypen, Driven coherent oscillations of a single electron spin in a quantum dot, Nature 442, 766-771 (2006)
Title: AtomChips: Integrated circuits for matter waves
Date/Time: 16-Apr, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: AtomChips aim at the miniaturization and integration of quantum optics and atomic physics on to a single chip, analogous to electronic circuits. It combines the best of both worlds: The perfected manipulation techniques from atomic physics with the capability of nanofabrication. AtomChips promise to allow coherent manipulation of matter waves on the quantum level by using high spatial resolution electro magnetic potentials from structures on the atom chip or by employing adiabatic radio frequency (RF) or micro wave (MW) potentials [1]. The talk will give an overview of the recent advances in the concepts, fabrication and experimental realization of AtomChips by illustrating the many different tasks that can be performed using ultra cold or Bose-Einstein condensed (BECs) atoms manipulated on the chip. These range from measuring magnetic and electric fields with unprecedented sensitivity by observing the density modulations in trapped highly elongated 1d BECs [2], to fundamental studies of the universal properties in low dimensional systems like non equilibrium dynamics and coherence decay [3] or signatures of thermal and quantum noise [4] in one dimensional super fluids. This work was supported by the European Union integrated project SCALA, the DIP the FWF and the Wittgenstein Prize. [1] T. Schumm et al. Nature Physics, 1, 57 (2005); S. Hofferberth et al. Nature Physics, 2, 710 (2006) [2] St. Wildermuth et al. Nature 435, 440 (2005); S. Aigner et al. Science 319, 1226 (2008) [3] S. Hofferberth et al. Nature 449, 324 (2007) [4] S. Hofferberth et al. Nature Physics, 4, 489 (2008)
Title: Exploring the quantumness of light in a cavity
Date/Time: 02-Apr, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Cavity QED experiments are described, in which a beam of Rydberg atoms is used to manipulate and probe non-destructively microwave photons trapped in a very high Q superconducting cavity. We realize ideal quantum non-demolition (QND) measurements of photon numbers, observe the radiation quantum jumps due to cavity relaxation and prepare non-classical fields such as Fock and SchrÃ¶dinger cat states. Combining QND photon counting with a homodyne mixing method, we reconstruct the Wigner functions of these non-classical states and, by taking snapshots of these functions at increasing times, obtain movies of the decoherence process. We also observe that the coherent evolution of the field in the cavity is frozen when we measure non-destructively its photon number and we realize in this way a simple demonstration of the quantum Zeno effect. These experiments open the way to the implementation of quantum feedback procedures aimed at preserving over long time intervals the quantum coherence of non-classical states of radiation in a cavity.
Title: Black holes as mirrors
Date/Time: 26-Mar, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: I'll discuss information retrieval from evaporating black holes, assuming that the internal dynamics of a black hole is unitary and rapidly mixing. Instead of locking away information for a near eternity, black holes can reveal their information in Hawking radiation remarkably quickly. The resulting estimate of a black hole's information retention time, based on speculative dynamical assumptions, is just barely compatible with the black hole complementarity hypothesis. The reason these conclusions hold is that typical local quantum circuits generate highly efficient quantum error-correcting codes. (Joint work with John Preskill)
Title: The photon and the vacuum cleaner
Date/Time: 12-Feb, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Photonic quantum technologies are largely based on the effects of quantum interference coupled with the nonlinearities that can be induced by measurements. This means that attention must be paid to the character of the individual light particles that are used to build up large-scale entanglement. In turn, this requires the development of sources and detectors that can verify the quantum state of the light field in all its degrees of freedom. I shall discuss how "vacuum engineering" can be used to prepare pure-state single photon wavepackets using nonlinear optics and conditional detection. The efficacy of such methods of preparation is predicated on the ability to understand what it is that the detector is measuring, and I shall illustrate a procedure for fully characterizing a quantum detector using tomography, thereby verifying the measurement operations for the device.
Title: Ciphering Classical Chinese
Date/Time: 05-Feb, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: Once premodern European and Arabic cipherers started to leave the more pedestrian "physical" approaches to steganography behind, techniques of encryption in political, military, religious or private contexts consisted mainly in the transformative manipulation of a plaintext and the devision of adequate decoding keys. They were thus by and large tantamount to the evolution of ever more powerful mapping algorithms, and dependent on increasingly sophisticated insights into the distributional properties of letters and lexical roots occuring in alphabetically represented written language. In China, the topic of information secrecy has been discussed since the pre-imperial period. State institutions maintaining certain types of government information secret and laws regulating the punishment of its leakage were of great complexity already during the Qin and Han dynasties, and reached unsurpassed bureaucratic intricacies under the Ming. Nevertheless, actual coding procedures seem to have developed quite slowly throughout imperial Chinese history, in the public as well as the private sectors. After a short overview of the earliest anecdotal evidence related to the disguising of information in early Chinese military texts, my talk will concentrate on three techniques, which illustrate the difficulty of pre-modern encryption on the basis of a logographic writing system representing a largely monosyllabic, tonal language. These are (1) the so-called "character verification" method, described in the Northern Song Essentials from the Military classics by Zeng Gongliang (999-1078), which maps numbered military commands onto sequences of characters appearing in a memorized pentasyllabic poem, serving as the key; (2) a system inspired by the phonological categories of the Middle Chinese rhyme dictionary tradition, and ascribed to the famous anti-Japanese Ming general Qi Jiguang (1528-1588); (3) homophonic substitution and â€œsynthanalyticâ€ character manipulation in poetry and edicts, recorded, e.g. in documents from the Taiping rebellion. In a concluding discussion, the inhibitive role of the non-alphabetic writing system in the development of formalized coding procedures will be weighed against the influence, which the â€œnon-development of probabilistic thinkingâ€œ, i.e. the â€œlack of an exploratory serious playfulnessâ€œ (Mark Elvin) in China might have brought about.
Title: Quantum algorithm for solving linear systems of equations
Date/Time: 20-Jan, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Title: Schrodinger's cats and kittens : new tools for quantum communications
Date/Time: 03-Dec, 04:00PM
Venue: NUS University Hall Auditorium, Lee Kong Chian Wing, Level 2
Abstract: We describe recent experiments [1, 2, 3] manipulating the quantum state of femtosecond light pulses, in order to generate photon number states (Fock states with n= 1 or 2 photons), quantum superpositions of coherent states (SchrÃ¶dinger's cats and kittens [1, 2]), and non- gaussian entangled states [3]. We will also discuss possible applications of these new states for quantum communications. Wigner functions References [1] A. Ourjoumtsev et al., "Generating optical SchrÃ¶dinger kittens for quantum information processing", Science 312: 83-86 (2006 ) [2] A. Ourjoumtsev et al., "Generation of optical "SchrÃ¶dinger cats' from photon number states Nature 448: 784-786 (2007) [3] A. Ourjoumtsev et al. "Increasing entanglement between Gaussian states by coherent photon subtraction", PRL 98:030502 (2007)
Title: Precision Quantum Metrology
Date/Time: 02-Dec, 05:00PM
Venue: NUS University Hall Auditorium, Lee Kong Chian Wing, Level 2
Abstract: Quantum state engineering of ultracold matter and precise control of optical fields have allowed accurate measurement of light-matter interactions for applications ranging from precision tests of fundamental physics to quantum information science. State-of-the-art lasers now maintain optical phase coherence over one second. Optical frequency combs distribute this optical phase coherence across the entire visible and infrared parts of the electromagnetic spectrum, leading to direct visualization and measurement of light ripples. A new generation of light-based atomic clocks has been developed, with ultracold Sr atoms confined in a carefully engineered optical lattice offering unprecedented coherence times for light-matter interactions. The uncertainty of this new clock has reached 1 Ã— 10-16, a factor of 4 below the current best Cs primary standard. These developments represent a remarkable convergence of ultracold science, laser technology, and ultrafast science. Further improvements are still tantalizing, with quantum measurement and precision metrology combining forces to explore the next frontier.
Title: From Einstein Intuitions to Quantum Bits: A New Quantum Age?
Date/Time: 02-Dec, 04:00PM
Venue: NUS University Hall Auditorium, Lee Kong Chian Wing, Level 2
Abstract: In 1935, with co-authors Podolsky and Rosen, Einstein discovered an amazing quantum situation, where particles in a pair are so strongly correlated that SchrÃ¶dinger called them â€œentangledâ€. By analyzing that situation, Einstein concluded that the quantum formalism was incomplete. Niels Bohr immediately opposed that conclusion, and the debate lasted until the death of these two giants of physics, in the 1950â€™s. In 1964, John Bell produced his famous inequalities which would allow experimentalists to settle the debate, and to show that the revolutionary concept of entanglement is indeed a reality. Based on that concept, a new field of research has emerged, quantum information, where one uses entanglement between qubits to develop conceptually new methods for processing and transmitting information. Large scale practical implementation of such concepts might revolutionize our society, as did the laser, the transistor and integrated circuits, some of the most striking fruits of the first quantum revolution, which began with the 20th century.
Title: Bose-Einstein Condensation, Classical Fields and Decaying Vortices
Date/Time: 02-Oct, 04:00PM
Venue: Physics Conference Room S13, Level M
Abstract: While all experiments with ultra cold atomic gases are performed at finite, nonzero temperatures most theory papers are assuming a temperature of zero Kelvin. We have developed a simple approximation which is applicable to a gas at nonzero temperature. It treats the atomic field as a c-number rather than as an operator. We call this â€œthe classical field approximationâ€. In my lecture I will explain the classical field approximation. I will compare this approximation and the exact quantum solution for a simple case of the ideal Bose gas. In the last part I will apply the method to multiply charged vortices, where some recent experiments are available. Recommended Pre-reading Materials: M. Brewczyk, M. Gajda, and K. RzÄ…Å¼ewski, Classical fields approximation for bosons at nonzero temperature, Journ. of Physics B 40, R1-R37 (2007)
Title: Optical Lattice Immersions for Direct Quantum Simulations
Date/Time: 28-Aug, 04:00AM
Venue: Physics Conference Room S13, Level M
Abstract: I will investigate the properties of atoms which are trapped in an optical lattice and immersed into a Bose-Einstein condensate (BEC). I will show that interspecies interactions lead to dephasing of the lattice atoms and, via BEC phonons, mediate an attractive interaction between them. This may cause lattice atoms to aggregate into a cluster. I will also study the impact of the BEC on transport properties and find a crossover from coherent behaviour described by an extended Hubbard model to diffusive hopping. Furthermore I will show that weak attractive interspecies interactions may give rise to instabilities. I will discuss the relation of this atomic lattice immersion to condensed matter systems and how it may be used for direct quantum simulations. Finally, I will extend these considerations to moving and rotating Bose-Einstein condensates and show how magnetic phenomena can be simulated in lattice immersions.
Title: Quantum Phase Transitions in Arrays of Coupled QED Cavities
Date/Time: 17-Jul, 04:00PM
Venue: Physics Conference Room S13, Level M
Abstract: Recent proposals of realizing condensed phases in cavity-QED like systems opened a number of new exciting possibilities in the physics of strongly interacting photonic systems. Arrays of coupled QED cavities have been shown to have superfluid, insulating and glassy phases. They can be used for transferring quantum information and for simulating interacting spin systems. Coupled cavities can be realized in a wide range of physical systems, from nanocavities in photonic crystals to Cooper pair boxes in superconducting resonators. After a brief introduction to the field, I will review the main features of the phase diagram and of the signatures of the various phases. I will discuss how, in principle, it might be possible to distinguish between the different phases by measuring photons fluctuations. I will finally discuss dynamical instabilities in these arrays when control parameters are varied in time.
Title: Open Quantum Systems, Entanglement, and the Laser Quantum State
Date/Time: 29-May, 04:00PM
Venue: Physics Conference Room S13, Level M
Abstract: An introduction to the treatment of open quantum systems as stochastic scattering processes (quantum trajectories) will be presented, together with some applications to illustrate the ideas. The final application will address the question: is optical coherence in fact a fiction [Moelmer, PRA 55, 3195 (1997)] or rather more fact than fiction [Noh and Carmichael, PRL 100, 120405 (2008)]?
Title: Cavity QED: Quantum Control with Single Atoms and Single Photons
Date/Time: 17-Apr, 04:00PM
Venue: S16 - LT31
Abstract: Over the past two decades, strong interactions of light and matter at the single-atom and single-photon level have enabled a wide set of scientific advances in quantum optics and quantum information science. Single, ultra-cold atoms can now be made to interact strongly and controllably with single-photon light fields confined within microscopic optical resonators (cavity quantum electrodynamics, or cavity QED). Moreover, new resonator configurations, such as lithographically-fabricated monolithic microresonators, hold great promise for the implementation of quantum networks and quantum logic with atoms and photons. In this colloquium I describe some elementary cavity QED systems and potential applications of these systems in quantum information processing. This includes recent theoretical and experimental results for cavity QED with toroidal microresonators.
Title: New Developments in Measurement-Based Quantum Computation
Date/Time: 27-Mar, 04:00PM
Venue: S16 - LT31
Abstract: Quantum computers offer a promising new way of information processing, in which the distinguishing features of quantum mechanics can fruitfully be exploited. Next to the standard quantum circuit model, various other models for quantum computation exist. Although these models have been shown to be formally equivalent, their underlying elementary concepts, as well the requirements for their practical realization, differ significantly. Exciting perspectives are offered by the new paradigm of measurement-based quantum computation, where the processing of quantum information takes place by rounds of simple measurements on a system of spins prepared in a highly entangled state. In this talk I will discuss a number of recent developments in measurement-based quantum computation on both fundamental and practical issues, e.g. regarding the power of quantum computation and its relation to entanglement, as well as steps toward its experimental realization. Furthermore, I will highlight the various ways in which this field is connected to other branches in physics and mathematics.
Title: Implementation of Basic Quantum Information Processing
Date/Time: 28-Feb, 04:00PM
Venue: S16 - LT31
Abstract: Quantum information processing is one of the most promising research areas for its possibility of bringing a revolutionary change in the information society. To realize it, however, there are several fundamental issues to be examined, namely, how to protect the quantum information from environmental noise, how to realize one-way computation using the cluster states, and how to guarantee the security of quantum cryptography under realistic noise and imperfection of the devices. In this talk I will introduce the basics of these issues and will describe the possible solutions mainly with photons including activity in my research group in Osaka University.
Title: Quantum Teleportation and Nonlocality
Date/Time: 10-Jan, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Title: Quantum Information: from burlesque ideas to a new technology
Date/Time: 08-Dec, 06:00PM
Venue: NUS University Hall Auditorium, Lee Kong Chian Wing, Level 2
Title: Ensemble encoding of quantum registers for quantum computing and communication
Date/Time: 24-Feb, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: In the conventional lay-out of a register for quantum computing, all qubits are associated with individual two-level quantum systems. Individual addressing and interaction with these systems permit one-bit gates, while a controllable pair-wise interaction between systems is needed to accomplish two-bit gates. We present a different approach that encodes a multi-bit quantum register in the collective internal state populations of an ensemble of identical multi-level quantum systems. This method establishes a linear relationship between the number of bits and the internal state Hilbert space dimension. It does not require experimental access to individual particles, but it relies on an interaction that restricts the collective populations to the (bit-) values zero and unity. We devote a detailed discussion to applications with neutral atoms interacting via Rydberg excited states, and we show that, e.g., a small cloud of cesium atoms may be operated as a universal quantum computer with up to 14 bits and as a deterministic multi-mode photonic device. Other schemes for collective encoding of quantum registers in hybrid quantum systems will be briefly discussed.
Title: The past of a quantum particle in our many-worlds universe
Date/Time: 07-Oct, 04:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: I will argue that if we want to believe that physics of today can explain everything, we have to accept existence of parallel worlds in our Universe. I will explain how to see an object without light and why an attempt prove, without light, that an object is absent, fails. This will demonstrate that Wheeler's approach to the past of a quantum particles does not explain the weak trace it leaves and that the proper description of the past of a quantum particles requires addition of a quantum state evolving backward in time.
Title: Position-based Cryptography
Date/Time: 07-Dec, 04:00PM
Venue: NUS Kent Ridge, University Hall Auditorium, Level 2, Lee Kong Chian Wing
Title: CQT CS Talk by Ronald Cramer, CWI & Leiden University
Date/Time: 01-Nov, 02:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: We present a new zero-knowledge protocol for proving knowledge of short preimages under additively homomorphic functions that map integer vectors to an Abelian group. The protocol achieves amor- tized efficiency in that it only needs to send O(n) function values to prove knowledge of n preimages. Furthermore we significantly improve previous bounds on how short a secret we can extract from a dishonest prover, namely our bound is a factor O(k) larger than the size of secret used by the honest prover, where k is the statistical security parameter. In the best previous result, the factor was O(k^{log k}n). Our protocol can be applied to give proofs of knowledge for plaintexts in (Ring-)LWE-based cryptosystems, knowledge of preimages of homomor- phic hash functions as well as knowledge of committed values in some integer commitment schemes. Joint work with Ivan Damgard, Chaoping Xing and Chen Yuan.
Title: CQT Colloquium by Nobuyuki Imoto, Osaka University
Date/Time: 02-Nov, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: If a high-quality entanglement is shared between two distant parties, there are a lot of innovative things we can do such as device-independent QKD, which is in fact initiated by Ekert [1]. For this, faithful quantum communication via a noisy and lossy channel is an important element, which is the main research item of my research group [2]. As we proceed this type of research, we encounter some fundamental research themes. For example, we developed a frequency converter of a single photon that maintains coherence and entanglement [3]. Our frequency converter acts as a beamsplitter in frequency domain, whose conversion efficiency is tunable. Using this frequency-domain beamsplitter, we performed Hong-Ou-Mandel interference [4], where two different-color input photons are converted into two same-color output photons whose color stochastically becomes either of the original two colors. We also performed Mach-Zehnder interference [5], which, in frequency domain, is more difficult than the HOM interference. The second example of fundamental research themes, other than the frequency converter, is cheat-sensitive type communication [6], where we can guess the result of the measurement performed by our partner regardless whether he/she chose from the linear and circular polarization measurements, which at first glance appears to be in conflict with the uncertainty principle. The key is that we not only prepare the initial state of the photon before the partnerâ€™s measurement but also measure its final state after the partnerâ€™s measurement. This concept is generalized to so-called weak value [7], and we are pursuing the meaning and usage of this new concept [8]. [1] A. K. Ekert, PRL67, 661 (1991). [2] T. Yamamoto et al., Nature 421, 343-346 (2003); Nat. Photon. 2, 488 - 491 (2008). [3] R. Ikuta et al., Nat. Commun. 2, 1544 (2011). [4] T. Kobayashi et al., Nat. Photon. 10, 441â€“444 (2016). [5] T. Kobayashi et al., Optics Express, 25, 012052_1_9 (2017). [6] K. Shimizu et al., PRA84, 022308 (2011). [7] Y. Aharonov et al., PRL, 60, 1351 (1988). [8] K. Yokota et al., New J. Phys. 18, 123002 (2016).
Title: CQT Talk by Patrizia Vignolo, InPhyNi Lab in Nice
Date/Time: 08-Nov, 12:30PM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: One dimensional (1D) strongly correlated quantum systems are nowadays the subject of intense theoretical and experimental activity due to the incredible experimental control offered by ultra-cold atoms setups. In such systems, the momentum distribution is a powerful probe of both gas statistics and of the intertwined effect of interactions between particles and the effective dimensionality they move in. A remarkable momentum distribution feature, in all dimensions, is the presence of universal power-law tails n(k)~k^{-4} for a gas where interactions can be schematized as contact ones (as it is the case for most standard cold gases experiments). The weight of such tails, denoted as Tanâ€™s contact, can be put into relation with several many-body quantities, ranging from the interaction energy to the depletion rate by inelastic collisions. In this work, we show that such tails also encode precious information about the permutational symmetry hiding behind the formation of magnetic-like structures in strongly-interacting multi-component Fermi gases. More in details, we combine an exact solution at infinite interactions and numerical Matrix-Product-State (MPS) simulations at finite interactions, in order to predict the behavior of the momentum distribution tails for a mixture of k fermionic components under 1D harmonic confinement and interacting among each other with completely SU(k)-symmetric repulsive contact interactions. We show that both the ground and excited states of the system have a well defined symmetry, thus indicating magnetic-like properties of the mixture, and that such information is fully encoded in the Tanâ€™s contact.
Title: Flexible, stretchable waveguides for quantum optics
Date/Time: 09-Nov, 02:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: In recent years the quantum optics community has become well acquainted with the advantages offered by an integrated, waveguide-based approach to optical circuits. Many prominent experimental results have benefited from the interferometric stability and easy access to large numbers of spatial modes offered by these systems. In most cases however, the waveguide platforms in use lack good options for tunability or constrain the polarization of propagating light. In response to these limitations, we have collaborated with JosÃ© Viana-Gomes' group at the CA2DM to develop an approach based on the soft polymer polydimethyl siloxane (PDMS). Our platform supports polarization insensitive guiding and allows a novel form of tuning via mechanical deformation of the optical circuit. In this talk I will discuss some unique features of this platform, and highlight experimental results in the form of a broadband tunable beamsplitter and a series of tunable quantum random walks. I will also outline the current direction of our research, with prospects for tunable entangled photon random walks and the inclusion of optical nonlinearity.
Title: Foundations of Lattice-based Cryptography
Date/Time: 23-Nov, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Lattice-based cryptosystems are perhaps the most promising candidates for post-quantum cryptography as they have strong security proofs based on worst-case hardness of computational lattice problems and are efficient to implement due to their parallelizable structure. Attempts to solve lattice problems by quantum algorithms have been made since Shorâ€™s discovery of the quantum factoring algorithm in the mid-1990s, but have so far met with little success if any at all. The main difficulty is that the periodicity finding technique, which is used in Shorâ€™s factoring algorithm and related quantum algorithms, does not seem to be applicable to lattice problems. In this talk, I will survey some of the main developments in lattice cryptography over the last decade or so. The main focus will be on the Learning With Errors (LWE) and the Short Integer Solution (SIS) problems, their ring-based variants, their provable hardness under the intractability assumptions of lattice problems and their cryptographic applications.
Title: CQT10 Conference
Date/Time: 07-Dec, 09:00AM
Venue: NUSS Guild House, NUS, Singapore
We welcome all to join us for a conference 7-8 December to mark our tenth anniversary. This event will be in the spirit of the scientific symposium we have held in previous years on our birthday, extended into a two-day event.
Title: Holographic Reconstruction of Single Photon Spatial Wavefunction
Date/Time: 09-Nov, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: The spatial structure of a single photon has proved to be indispensable resource allowing the experimental realization of free-space quantum cryptography or high dimensional entanglement. Although efficient methods for manipulating spatial characteristic of individual photons can be easily transferred from the field of classical optics, their spatial structure cannot be measured using the standard interferometric reference-based methods due to their completely undefined-global phase. Here we present and experimentally demonstrate a different approach based on spatially resolved detection of two-photon interference. Although such measurements are usually perceived to be insensitive to the phase difference between two interfering photons we show that rarely considered local phase dependence can be still observed and utilized for direct recovery of a single photon quantum wavefunction.
Title: Macroscopic quantum superpositions in thermalizing and many-body localized systems
Date/Time: 14-Dec, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: The decoherence program explains why it is hard to observe quantum superpositions in macroscopic scales although their existence is not excluded by the laws of quantum mechanics. This explanation is based on the openness of quantum systems but a question of whether a macroscopic superposition in an isolated system is stable remains. Recently, it has been shown that isolated quantum systems can thermalize in the sense that an expectation value of local observables after a long time evolution gives the same value with the thermal ensemble-averaged values. However, not all system thermalizes. One such example is a many-body localized (MBL) system which does not thermalize due to random disorders in spite of present interactions between particles. In this talk, we first show that macroscopic superpositions in an isolated system disappear when it thermalizes. We use a well-established measure of quantum macroscopicity and the eigenstate thermalization hypothesis to obtain this result. We next investigate an MBL system and show that local integrals of motion arise in an MBL system may preserve a macroscopic superposition. Consistent extensive numerical results are also demonstrated using the disordered Heisenberg model.
Title: CQT CS Talk by Priyanka Mukhopadhyay, CQT
Date/Time: 15-Aug, 08:21PM
Venue: CQT Level 4 Meeting Room, S15-04-03
Abstract: We modify the randomized sieving algorithm of Ajtai, Kumar and Sivakumar[2001,2002] to solve SVP and CVP in the L infinity norm, that results in substantial quantitative improvement over prior results. In each iteration of the sieving sub-routine of the AKS algorithm, given a set S of lattice vectors we maintain a list C of vectors as centres and for each of the remaining vector v in S. we search for a vector that is within a certain distance from it and thus the difference of the two gives a vector of reduced length. We make a simple but powerful observation that for the special case of the L infinity norm, if we partition the ambient space [-R, R]^n into ([-R, -R + \gamma), [-R + \gamma, -R+2\gamma), ... )^n, then it is easy to see that each such partition will contain at most one centre. Given v in S, we can find its partition by checking the interval in which each co-ordinate belongs and then check whether this partition contains a centre. This drastically improves the running time for the sieving procedure in the SVP algorithm from |S| |C| to |S| n. We then use the same idea to obtain significantly faster approximation algorithms for both SVP and CVP. Along the way, we optimize several steps specialized to the case of L infinity norm in the analysis of these algorithms. We also show that the heuristic sieving algorithms of Nguyen and Vidick[2008] and Wang et.al.[2011] can also be analyzed in the L infinity norm. This work has been done with Divesh Aggarwal.
Title: The enigma: do fundamental constants of nature vary in time?
Date/Time: 11-Dec, 12:00PM
Venue: CQT Level 3 Seminar Room, S15-03-16
Abstract: The father of the Turing machine was interested in the question of the possible variation in time of the fundamental constants of nature: for example, that of the Newtonian constant of gravitation. This is discussed in Andrew Hodge's biography, "Alan Turing: The Enigma" (Simon & Schuster, 1983), that is the source of the film, "The Imitation Game" (2014). After finding a clue to this question in Turing's paper that first introduced the concept of the Imitation Game ("Computing Machinery and Intelligence," Mind 59, 433 (1950)), we shall explore how it can even be asked, with particular reference to the forthcoming redefinition of the International System of Units.
Title: Tutorial on SDP formulation of the adversary bound and its dual.
Date/Time: 10-Jan, 02:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: In this tutorial I will show how to express the adversary bound as a semi-definite program. Then I will show how to obtain its dual, whose solutions (commonly called span programs) are known to yield optimal quantum query algorithms.
Title: CQT PhD Oral Defense by Ewan Munro
Date/Time: 14-Dec, 11:30AM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: Thanks to recent experimental advances, quantum light-matter interactions in atomic ensembles can now be studied in regimes that have hitherto been inaccessible. A prominent example involves atoms coupled to a photonic band gap material, which strongly modifies the atomic emission and absorption properties compared to free space, and can mediate effective dipole-dipole interactions with rich spatial properties. The first part of this thesis describes theoretically the fundamental optical properties of such a system, including important characterisation tools in the linear regime, and potential applications leveraging strong non-linearity at the few-photon level. A second example involves atoms in free space arranged in optical tweezer arrays, where highly ordered lattices of atoms can be assembled. In such platforms, strong interference in light scattering can give rise to remarkable collective optical phenomena. The second part of this thesis shows how strong dipole-dipole interactions can manifest themselves in the steady-state population distribution of a driven 1D array of multilevel atoms.
Title: Julian Schwinger Centennial Conference
Date/Time: 07-Feb, 09:00AM
Venue: NUSS Guild House, NUS, Singapore
Julian Schwinger (February 12, 1918 - July 16, 1994) is best known for his work on the theory of quantum electrodynamics (QED), in particular for developing a relativistically invariant perturbation theory, and for renormalizing QED to one loop order. For his substantial contributions to many areas, he is widely recognized as one of the greatest physicists of the twentieth century. Along with Feynman and Tomonaga, he won the 1965 Nobel Prize in Physics for his work on quantum electrodynamics. Starting as a leader in nuclear physics, the discoverer of tensor forces, Schwinger pioneered powerful variational methods in classical electrodynamics and was the American developer of the theory of synchrotron radiation. He is responsible for much of modern quantum field theory, including a quantum version of the action principle, and the equations for the Green's functions that define the content of such theories. He laid the foundations for non-equilibrium quantum statistical mechanics and for quantum gravity. He developed the first electroweak model, an SU(2) gauge group spontaneously broken to electromagnetic U(1) at long distances. He also explored the first example of confinement in the Schwinger model, quantum electrodynamics in 1 + 1 dimensions. He was responsible for the theory of multiple neutrinos, Schwinger terms, the theory of the spin-3/2 field, and discovered anomalies in quantized fields. He advanced the theory of magnetic charge, monopoles and dyons. As Schwinger contributed to many more areas in classical and quantum physics, the above is just selection of topics.
Title: New tools to investigate non-classical correlations
Date/Time: 21-Dec, 03:00PM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: We are primarily interested in correlations being inherent of quantum mechanics and absent in any local realistic model. We would like to present our developments on techniques to study contextuality and entropic Bell inequalities. In more detail, we propose a new approach to investigate a state-independent contextuality. It uses only one copy of system, does not require a state preparation and has the advantage that it admits noisy measurements. We alsoreport a successful experiment performed according to our idea. In the case of entropic Bell inequalities we show that it is more suitableto use the Tsallis entropy than the Shannon entropy, because it reveals non-classicality for a larger set of quantum states. Moreover, we present a new application of a method that is used to deriveentropic Bell inequalities to nd new bounds on the correlation between non-commuting observables.
Title: Scalable quantum computing withsimple and complex atoms
Date/Time: 18-Jan, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Quantumcomputing is a few decades old and is currently an area where there is greatexcitement, and rapid developments. A handful of distinct approaches have shownthe capability of on demand generation of entanglement and execution of basicquantum algorithms.
Oneof the daunting challenges in developing a fault tolerant quantum computer isthe need for a very large number of qubits. Neutral atoms are one of the mostpromising approaches for meeting this challenge. I will give a snapshot of thecurrent status of atomic quantum computing, describe the physics underlyingneutral atom qubits and Rydberg state mediated quantum gates, and show how oneof the most complicated atoms in the periodic table may lead to some simplesolutions to hard problems.
Title: Spin-resolved microscopy of doped Hubbard chains
Date/Time: 23-Jan, 11:00AM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: The doping of an antiferromagnet can lead to complex physics related to high temperature superconductivity. In one dimension, however, the relevant competition between spin and density sectors is largely absent due to the separation of the spin and density modes at low energy. With our quantum gas microscope for ultracold sermonic Li-6, we can study of such systems with a unique control over kinetic energy, interactions and doping. A challenge has been to reach the required temperature for spin order and to measure the antiferromagnetic correlations with cold atoms. I will present our direct, single-atom resolved detection of antiferromagnetic correlations in spin-1/2 Hubbard chains [1]. Upon doping the order decreases and their periodicity becomes incommensurate when measured with a standard two-point correlator. With our full access to the spin and density distribution, we can directly measure three-point spin-hole-spin correlations and thus confirm that a hole in 1d only acts as a domain boundary of the spin-sector [2]. This is a direct consequence of the phenomenon of spin-charge separation and it allows to reveal the full correlations with non-local string operators [3]. Our technique can be extended to measure spin-charge separation dynamically and we are starting to study the complex interplay between magnetic order and density fluctuations in higher dimensions. References 1. M. Boll et al., Science 353, 1257â€“1260 (2016). 2. T. A. Hilker et al., Science 357, 484-487 (2017). 3. M. Den Nijs & K. Rommelse Phys. Rev. B 40, 4709â€“4734 (1989)
Title: Entanglement and coherence in quantum statemerging
Date/Time: 19-Dec, 02:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Understanding the resource consumption in distributedscenarios is one of the main goals of quantum information theory. A prominentexample for such a scenario is the task of quantum state merging where twoparties aim to merge their parts of a tripartite quantum state. In standardquantum state merging, entanglement is considered as an expensive resource,while local quantum operations can be performed at no additional cost. However,recent developments show that some local operations could be more expensivethan others: it is reasonable to distinguish between local incoherentoperations and local operations which can create coherence. This idea leads usto the task of incoherent quantum state merging, where one of the parties hasfree access to local incoherent operations only. In this case the resources ofthe process are quantified by pairs of entanglement and coherence.
Here, we develop tools for studying this process, andapply them to several relevant scenarios. While quantum state merging can leadto a gain of entanglement, our results imply that no merging procedure can gainentanglement and coherence at the same time. We also provide a general lowerbound on the entanglement-coherence sum, and show that the bound is tight forall pure states. Our results also lead to an incoherent version of Schumachercompression: in this case the compression rate is equal to the von Neumannentropy of the diagonal elements of the corresponding quantum state.
Title: Quantum Communication and Imaging with Photons
Date/Time: 10-Jan, 11:00AM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: Quantum technology is believed to the next revolution of information processing. In this talk, I will present two important advances in quantum information processing: quantum communication and single-photon imaging. (i) Quantum communication can provide unconditional security for data transmission. In the first part, I will present our theoretical and experimental developments in quantum cryptography, including measurement-device-independent quantum key distribution (MDI-QKD), Si photonic-chip based QKD and quantum random number generator (QRNG). (ii) Single-photon imaging involves the detection and timing of single photons to beat classical limits. In the second part, I will address how to perform accurate 3D imaging with a single-photon camera at a light level of one photon per pixel. Our novel photon-efficient imaging systems can allow us to achieve long-range dynamic sensing, see around corners and push the limits of imaging technology in widespread applications.
Title: Single ion detection theory, and a thermodynamic cycle experiment
Date/Time: 10-Jan, 11:00AM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: In quantum information technology, the feasibility of coupling trapped ion qubits to solid-state systems is an active area of research. I will present two theoretical results related to this subject. The first result is a method to measure the average phonon number of a trapped ion, using an electronic technique, rather than the conventional optical technique. The second result aims to answer the question: â€œIs it possible to entangle two ions in separate traps, using a conducting wire placed between them?â€ In addition, I will describe an experimental plan to perform a complete, single-ion quantum thermodynamic cycle. In the field of quantum thermodynamics, where questions about efficiency and coherence in such processes persist, this will help place the similarities and contrasts with classical thermodynamic cycles on firmer ground. The main ideas will be outlined briefly, along with some of our group's results in this direction. One personal contribution, the design and implementation of a helical resonator operating at 25MHz and a total capacitance (resonator + trap) of ~40pF, will then be discussed in more depth. By identifying the important parameters and limitations of helical resonators, conclusions can be drawn about the frequency and capacitance regimes in which ion traps can and cannot be built.
Title: Notable Designs in Post-Quantum Cryptography
Date/Time: 16-Jan, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: The most prominent public-key cryptosystems in current use are based mainly on two mathematical problems: integer factorisation or discrete log. The best classic algorithms for tackling these problems have subexponential complexity, a fact that underpins the security of much of modern digital communication. In 1994 Peter Shor proposed a quantum algorithm which can however solve these problems in polynomial time, prompting the cryptographic community to work on the development of so-called â€œpost-quantum" cryptography, i.e. cryptographic schemes whose security are based on problems for which there are no known quantum speed-up. The recent (and projected) progress in building scalable and reliable quantum computers has provided fresh stimulus to this field, culminating in the current NIST PQ Standardisation Process: a NIST-led public effort to design, evaluate and eventually standardise one or more quantum-resistant public-key cryptographic algorithms. NIST received 82 submissions by the deadline on 30 Nov 2017, and currently over 60 algorithms are being scrutinised by the cryptographic community. In this talk we give a brief overview of the main â€œclassesâ€ of post-quantum cryptographic algorithms, focusing later on one of the most popular designs: cryptographic schemes based on error-correcting codes.
Title: Modes and States in Quantum Optics
Date/Time: 31-Jan, 03:30PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Quantum Optics, as the child of Optics and Quantum Mechanics, has inherited a double linearity: that of Maxwell equations, which use optical modes as a basis of solutions, and that of the SchrÃ¶dinger equation, which uses quantum state bases. Considering these two bases on an equal footing and tailoring quantum fields not only in given modes, but also optimizing the spatiotemporal shapes of the modes in which the state is defined, opens new ways for characterizing and exploiting complex quantum states. We will describe several applications of this approach in quantum information processing and quantum metrology.
Title: Ultracold 6Li40K Polar Molecules
Date/Time: 22-Jan, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract : The long range anisotropic interaction between ultracold polar molecules makes them suitable systems for the research of many body physics and quantum simulation. The ultracold 6Li40K ground state molecule has a larger electric dipole moment than the other bi-alkali molecules that have been published. We want to transfer our weakly bound 6Li40K Feshbach molecules to their absolute ro-vibrational ground state. We plan to study the chemical reactions between these ground state molecules by tuning the dipole-dipole interaction and to investigate many body physics.
Title: Non-equilibrium quantum simulation with ultracold atoms
Date/Time: 02-Feb, 02:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Many-body systems out of equilibrium can host numerous intriguing phenomena such as time crystals, quantum chaos, or dynamical phase transitions. To explore one such dynamical phase transition, we engineer a quantum simulator of the collective Heisenberg model with a local longitudinal field. Using the two lowest hyperfine states of a Fermi-degenerate gas of potassium (40K) atoms, we tune the s-wave scattering to be weak enough to freeze motion in single-particle eigenstates. We initialize a coherent superposition with maximal transverse magnetization, and measure magnetization dynamics using a Ramsey sequence. We observe a dynamical phase transition between two steady states: an ordered ferromagnetic state, where the transverse magnetization is stabilized by a large energy gap, and a demagnetized state. We explore the dynamical phase diagram of the model by tuning both interaction strength (with a Feshbach resonance) and inhomogeneity variance (with vector light shifts). We also validate experimentally a spin model description of the dynamics. We find excellent agreement with theoretical calculations based on a mean-field treatment of the Heisenberg model. The observed stabilization of many-body coherence over long times opens a new window for the generation of correlated quantum states in fermions, with applications to enhanced metrology and advanced materials.
Title: (Gap/S)-ETH Hardness of SVP
Date/Time: 24-Jan, 02:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: There has been a lot of research in the last two decades on constructing cryptosystems whose security relies on the hardness of the shortest vector problem (SVP) on integer lattices. The SVP is well known to be NP-hard. However, such hardness proofs tell us very little about the quantitative or fine-grained complexity of SVP. E.g., does the fastest possible algorithm for SVP still run in time at least, say, 2^{n/5} , or is there an algorithm that runs in time 2^{n/100} or even 2^{\sqrt{n}}? The above hardness results cannot distinguish between these cases, but we certainly need to be confident in our answers to such questions if we plan to base the security of widespread cryptosystems on these answers. In this talk, I will give a partial answer to this question by showing the following quantitative hardness results for the Shortest Vector Problem in the \ell_p norm (SVP_p) where n is the rank of the input lattice. 1) For "almost all'' p > 2.14, there no 2^{n/C_p}-time algorithm for SVP_p for some explicit constant C_p > 0 unless the (randomized) Strong Exponential Time Hypothesis (SETH) is false. 2) For any p > 2, there is no 2^{o(n)}-time algorithm for SVP_p unless the (randomized) Gap Exponential Time Hypothesis (Gap-ETH) is false. 3) There is no 2^{o(n)}-time algorithm for SVP_2 unless either (1) (non-uniform) Gap-ETH is false; or (2) there is no family of lattices with exponential kissing number in the \ell_2 norm. This is joint work with Noah Stephens-Davidowitz.
Title: Coupling 1D Atom Arrays to an Optical Nanofiber: Platform for Waveguide QED experiments
Date/Time: 25-Jan, 11:00AM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: The coupling of cold atoms to 1D nanoscale waveguides have opened new avenues of research. The waveguide in our case is a nanofiber, which confines light transversally to a subwavelength scale. The guided light exhibits a strong evanescent field allowing enhanced atom-photon interaction in the vicinity of nanofiber. In our experiment, a cold atomic cloud is first interfaced with an optical nanofiber. By using an optical lattice in the evanescent field, the atoms are then trapped in 1D atomic arrays close to the nanofiber. In this platform, we reach high optical depth OD ~ 100 and long lifetimes ~ 25 ms by using a dual-color compensated trapping scheme that preserves the internal properties of atoms. Recently, we have demonstrated the creation of a heralded single collective excitation in the trapped ensemble of atoms using DLCZ protocol. Subsequently, the excitation has been converted into a single photon in the guided mode with high efficiency. Non-classical correlations between photon pairs have been observed in the experiment. In another experiment, we have explored the collective effects emerging from the spatial ordering of atoms. When the period of the lattice is made close to commensurate with the resonant wavelength, Bragg reflection, as high as 75%, is observed. The reflection shows dependency on orientation of the probe polarization relative to the atomic arrays - a chiral signature in nanoscale waveguide-QED systems. The ability to control photon transport in 1D waveguides coupled to spin systems would enable novel quantum networking capabilities and the study of many-body effects arising from long-range interactions.
Title: Promise Constraint Satisfaction
Date/Time: 25-Jan, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Given a 5-SAT instance admitting an assignment satisfying at least 2 literals in each clause, can one efficiently find a satisfying assignment that sets at least one literal to true in each clause? Given a 5-uniform hypergraph admitting a red-blue coloring of its vertices with exactly two red vertices in each hyperedge, can one efficiently find a red-blue coloring that leaves no hyperedge monochromatic? Given a graph admitting a homomorphism to the 7-cycle, can one efficiently 3-color it? The answers to these questions are: No (unless P=NP), yes, and open respectively. These are examples of *promise* constraint satisfaction problems (PCSP), where in the decision version, we need to distinguish instances satisfiable according to one set of predicates, from those that are unsatisfiable even under relaxed versions of those predicates. PCSPs generalize normal CSPs where the two sets of predicates are identical. The (recently resolved) famous dichotomy conjecture states that every CSP is either polytime decidable or NP-hard. Further, the tractable cases are precisely those admitting closure operations (called â€œpolymorphismsâ€) that preserve the predicates defining the CSP. The landscape of PCSPs reveals several new phenomena and challenges on both the algorithmic and hardness fronts compared to the CSP world. This talk will describe some of our forays into better understanding PCSPs, which revolve around the notion of â€œweak polymorphisms.â€ We will sketch our hardness proof (with P. Austrin and J. HÃ¥stad) for the above promise k-SAT problem, based on a characterization of the weak polymorphisms as juntas. We will discuss a body of work (with J. Brakensiek) that develops the weak polymorphism framework to establish a complexity dichotomy for the case of Boolean symmetric PCSP. Numerous intriguing problems about PCSPs and the state of polymorphisms remain open, and we will mention a couple of them.
Title: Analyzing n-cycle non-contextuality inequalities
Date/Time: 29-Jan, 04:00PM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: We analyze n -cycle non-contextuality inequalities and discuss the condition for the quantum violation for odd as well as even n-cycle. The set of quantum states for qutrits, which can violate odd n-cycle non-contextuality inequality, shrinks as we increase n . In the infinite n scenario, the only qutrit which violates the inequality is the maximally contextual state. For even cycle, the necessary condition for quantum violation depends on the difference of the largest and smallest eigenvalues for the two qubit density matrix Ï . If time permits, I will discuss the experimental results on IBM 5-qubit quantum computer.
Title: Adaptive Lower Bound for Testing Monotonicity on the Line
Date/Time: 31-Jan, 02:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: In the property testing model, the task is to distinguish objects possessing some property from the objects that are far from it. One of such properties is monotonicity, when the objects are functions from one poset to another. It is an active area of research within the field of property testing. Recently, Pallavoor, Raskhodnikova and Varma (ITCS'17) proposed an $\eps$-tester for monotonicity of a function $f\colon [n]\to[r]$, whose complexity depends on the size of the range as $O({\log r}/{\eps})$. In this talk, I will prove a nearly matching lower bound of $\Omega({\log r}/{\log \log r})$ for adaptive two-sided testers.
Title: Ion Traps Experiments at CIML (Aix-Marseille University, France)
Date/Time: 05-Feb, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Trapping of ions in radio-frequency (RF) ion traps is a topic of great interest for multiple applications [1]. Quantum information processing, frequency metrology, test of fundamental constants are among the many domains where ions in RF traps play a key role. In this presentation I will cover some of the recent work performed in the CIML group at Aix-Marseille University (France) regarding different aspects of ions confined in RF traps. The topics presented will be: the transport of large ion clouds in the non-adiabatic regime over macroscopic distances [2]; the crystallization of ions in an octopole trap in an unexpected fashion [3]; and finally, numerical simulations regarding the sympathetic cooling of Highly Charged Ions [4]. [1] Nobel prize in physics 1989, H. G. Dehmelt, P. Wolfgang: â€œfor the development of the ion trap techniqueâ€, www.nobelprize,org [2] J. Pedregosa-Gutierrez et al. IJMS 381 (2015), M. R. Kamsap et al. PRA 92, 043416 (2015) [3] J. Pedregosa-Gutierrez et al. Journal of Modern Optics (2017), M. R. Kamsap et al. PRA 95, 013413 (2017) [4] L. SchmÃ¶ger, et al., Science 347, 1233 (2015)
Title: Ultimate precision bound in the quantum estimation theory:
Explicit formula for the Holevo bound for qubit-state estimation problems
Date/Time: 22-Feb, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: In this talk, we first review an ultimate precision bound, the Holevo bound, for the problem of parameter estimation about quantum states. We discuss previously known cases where the Holevo bound is expressed explicitly in terms of a given model, i.e., quantum versions of Fisher information. The main contribution of this talk is to derive an explicit expression for the Holevo bound for estimating any two-parameter family of qubit mixed-states in terms of a given model. The obtained formula depends solely on the symmetric logarithmic derivative (SLD), the right logarithmic derivative (RLD) Fisher information, and a given weight matrix. One of the important results is that a general model other than special cases exhibits an unexpected property: The structure of the Holevo bound changes smoothly when the weight matrix varies.
Title: Advancements In Quantum Key Distribution At Telecom Wavelengths
Date/Time: 13-Feb, 02:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Quantum key distribution (QKD) is a core component of future telecommunication networks. It enables two distant parties to share a random encryption key without placing assumptions on an eavesdropperâ€™s capabilities. In particular, QKD at telecom wavelengths (1260 - 1625 nm) has the potential for fast deployment due to existing optical fibre infrastructure and mature telecom technologies. We are implementing such a system here in Singapore utilizing entanglement based protocols and single photon source/detectors that are compatible with the local fibre networks.
Title: Workshop on Quantum Algorithms and Complexity Theory 2018
Date/Time: 26-Feb, 10:30AM
Venue: CQT Level 3 Seminar Room, S15-03-15
This workshop gathers experts in randomized and quantum algorithms and complexity theory. The purpose of this 4.5 days workshop is to investigate interesting and important questions related to recent developments in randomized and quantum algorithms and complexity theory.
Details of the workshop: wqact.quantumlah.org
Title: Complexity Classification of Conjugated Clifford Circuits
Date/Time: 23-Feb, 03:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Clifford circuits â€” i.e. circuits composed of only CNOT, Hadamard, and Ï€/4 phase gates â€” play a central role in the study of quantum computation. However, their computational power is limited: a well-known result of Gottesman and Knill states that Clifford circuits are efficiently classically simulable. We show that in contrast, â€œconjugated Clifford circuitsâ€ (CCCs) â€” where one additionally conjugates every qubit by the same one-qubit gate U â€” can perform hard sampling tasks. In particular, we fully classify the computational power of CCCs by showing that essentially any non-Clifford conjugating unitary U can give rise to sampling tasks which cannot be simulated classically to constant multiplicative error, unless the polynomial hierarchy collapses. Furthermore, by standard techniques, this hardness result can be extended to allow for the more realistic model of constant additive error, under a plausible complexity-theoretic conjecture. This work can be seen as progress towards classifying the computational power of all restricted quantum gate sets. Based on arXiv:1709.01805 (joint work with Adam Bouland and Joseph F. Fitzsimons).
Title: Non-Equilibrium Superfluid Mixtures
Date/Time: 02-Mar, 11:00AM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: Mixtures of quantum fluids, or superfluids, are nowadays routinely generated in controlled environments of ultracold atomic gases: they can take the form of different internal states, different isotopes, or different elements, and can even be made up of systems obeying different quantum statistics. A first important property regards the co-existence of such superfluids: in particular, what sets the extent of spatial overlap between two interacting quantum gases? I will review experimental evidence of phase profiles, present the â€œbasicâ€ criterion routinely used to interpret them, and then critically assess its limitations, supported by extensive mean-field simulations. As I will show, a quantitative analysis of such experiments requires either a new criterion for in-situ imaging, or careful consideration of dynamical processes within the mixture: specifically, I will show that this transition can be mapped out experimentally by measuring the damping rate and the frequency of the dipole oscillations [1]. Presenting an extended kinetic model with full collisional damping [2], and implementing it to study the coupled expansion dynamics at different temperatures I will show how the homogeneous phase-separation criterion actually emerges dynamically in mixtures during expansion as a result of mechanical equilibrium across the condensate interface region, with the presence of a non-negligible gravitational sag found to be advantageous for identifying the (broad) transition region [3]. The relevance of such findings to â€œdual (Bose-Fermi) superfluidsâ€, and the role of growth dynamics in the establishment of the emerging phase profiles [4] will also be discussed. [1] Lee et al., PRA, 94, 013602 (2016); [2] Edmonds et al., PRA, 91, 011602(R) (2015); PRA 92, 063607 (2015); Lee et al., JPB, 49, 214003 (2016); [3] Lee et al., arXiv:1712.07481 (2017); [4] Liu et al., PRA 93, 023628 (2016).
Title: Cold dipolar bosons
Date/Time: 01-Mar, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: I will review recent research on the role of long range forces in quantum gases. I will mention experimental efforts in condensing chromium, erbium and dysprosium. I will describe in some detail the properties of just two dipolar atoms in a trap comparing magnetic and electric dipolar systems. Then I will talk about dipolar dark solitons, ending with our construction of a multi-particle roton state.
Title: A Lower Bound for Maximally Recoverable Codes with Locality
Date/Time: 21-Feb, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract:
MDS codes like Reed-Solomon codes enable erasure correction with optimal redundancy: with h redundant symbols they allow recovery of any subset of h erased positions. In matrix terms, they are defined by an h x n parity check matrix all of whose h x h submatrices are nonsingular. Such matrices, e.g. Vandermonde, exist over a field of size O(n).
The prevalent use of erasure coding in today's large distributed storage systems, where individual storage nodes often fail, brings to the fore a new requirement: the ability to quickly recover any single symbol of the codeword based on few other codeword symbols. Such "locality" can be built into the code via local parity checks --- for example, the n codeword symbols can be partitioned into n/r groups each with r symbols obeying a local parity check. Here r is the locality parameter of the code. In matrix terms, we have an (n/r + h) x n matrix with the first n/r rows, each with r 1's, corresponding to the local parity checks, and the last h rows unrestricted. The local checks compromise the MDS property, but we would still like the code to correct all erasure patterns that can possibly be recovered given the specified topology of parity checks. This property is called Maximal Recoverability, and for the above topology amounts to the nonsingularity of every (n/r+h) x (n/r+h) submatrix that includes at least one column from each local group.
The known constructions (and even existence proofs) of such matrices require a very large field size of about n^h, and it has been an important question whether MR codes can exist over smaller, even O(n)-sized, fields. The talk will mention the prior construction with n^h field size, and then present a recent super-linear lower on the field size which relies on known vertex expansion properties of the hyperplane-point incidence graph in projective space.
Based on joint work with Sivakanth Gopi and Sergey Yekhanin.
Title: Roton in a many-body dipolar system
Date/Time: 28-Feb, 11:30AM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: We solve exactly the many-body 1D model of atoms interacting via short range attractive and long range repulsive dipole-dipole forces. Periodic boundary conditions imply the conservation of total momentum. We find that the so-called yrast states, i.e. the lowest energy states with fixed total momentum, may contain elementary excitations known from the Bogoliubov approximation. In particular, we identify the celebrated roton state. With our exact methods we also go to stronger interactions, beyond the validity of Bogoliubov approximation.
Title: Superconducting qubits, the macroscopic atoms for building quantum processors
Date/Time: 28-Mar, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Quantum theory, formed in the early part of the last century, has revolutionized our view on the nature of physical reality. More than half a century after its inception, a few great minds of physics, including Richard Feynman, predicted that the laws of quantum mechanics could give rise to a computing paradigm that is far superior to classical computing for certain tasks. Decades have passed since their great insight, but controlling fragile quantum systems well enough to implement even the most primitive quantum computer has proven difficult. A promising way of making quantum bits (qubits) is by using superconducting Josephson junctions. Devices made out of these junctions show quantum properties at the macroscopic level, providing advantages in controlling and connecting qubits. In this talk, I discuss the prospects and challenges in making quantum processors by using superconducting qubits. I report on our progress at Google and explain how qubits can be used to study problems at the core of statistical mechanics; in particular, we studied the signatures of transition from ergodic to the many-body localized state in a chain of 9 qubits.
Title: Faster computing a short lattice basis
Date/Time: 21-Mar, 02:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Given as input two integers a and b, Euclid's algorithm outputs the positive generator gcd(a,b) of the ideal aZ+bZ. Computing a lattice basis is a classical high-dimensional generalization of the gcd problem: given integer vectors a_1, ... , a_n \in Z^m, find a Z-basis of the lattice L={\sum_{i=1}^{n} x_{i}a_{i}, x_i \in Z} generated by the a_{i}'s. It is well-known that such a basis can be found in polynomial time: the fastest algorithm known is an algorithm computing the Hermite normal form (HNF). However such HNF algorithms are usually not suitable for the applications where the output basis is required to be ``short'', i.e. not much longer than the input vectors. In this talk, we will present an algorithm which computes a basis guaranteed to be ``short'' (namely, the size of the output basis does not increase the size of the input generators by more than a factor linear in the dimension), and whose asymptotical running time matches that of the best HNF algorithms: in fact, it reduces the problem to two well-chosen HNF computations. We will emphasise the intuitive idea behind our algorithm.
Title: On Interesting Relations Between Continuous Non-Malleable Codes and Parallel CCA Commitments
Date/Time: 15-Mar, 02:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: In this work we construct the first continuous non malleable codes resistant to constant tampering and permutation tampering. We instantiate our codes with two different malleable codes to get codes of inverse polynomial and inverse logarithmic rate. We also use this stronger variant of non malleable codes to come up with stronger variants of non malleable commitments.
Title: MajuLab/CQT/NUS workshop on Localization, Quantum Chaos and Topology with Matter Waves
Date/Time: 20-Mar, 09:00AM
Venue: National University of Singapore
This is a mini-workshop on Localization, Quantum Chaos and Topology with Matter Waves. Find program at http://majulab.cnrs.fr/spip.php?article176.
The seminars rooms have limited space, please do register through EventBrite link: https://www.eventbrite.fr/e/workshop-on-localization-quantum-chaos-and-topology-with-matter-waves-tickets-43871880977 .
There are no registration fees.
Title: Thermodynamics of Modularity: Structural Costs Beyond the Landauer Bound
Date/Time: 16-Mar, 03:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract:
Complex computations typically occur via the composition of modular units, such as the universal logic gates found in logical circuits. The benefit of modular information processing, in contrast to globally integrated information processing, is that complex global information processing is more easily and flexibly implemented via a series of simpler, localized information processing operations that only control and change local degrees of freedom. We show that, despite these benefits, there are unavoidable thermodynamic costs to modularityâ€”costs that arise directly from the operation of localized processing and that go beyond Landauerâ€™s dissipation bound for erasing information. We quantify the minimum irretrievable dissipation of modular computations in terms of the difference between the change in global nonequilibrium free energy and the local (marginal) change in nonequilibrium free energy, which bounds modular work production. This modularity dissipation is proportional to the amount of additional work required to perform the computational task modularly, measuring a structural energy cost. It determines the thermodynamic efficiency of different modular implementations of the same computation, and so it has immediate consequences for the architecture of physically embedded transducers, which are information processing agents. Constructively, we show how to circumvent modularity dissipation by designing agents that capture the information reservoirâ€™s global correlations and patterns. We prove that these agents, when acting as pattern generators or extractors, must match the complexity of their environment to minimize the modularity dissipation. Thus, there are routes to thermodynamic efficiency by optimizing the modular architecture of computations.
Title: Quantum computers: how they work and what they'll mean for business
Date/Time: 29-Mar, 06:30PM
Venue: Impact Hub, Singapore, Level 1, 128 Prinsep Street
Abstract: Quantum computing was ranked as one of the top 10 breakthrough technologies in 2017 by MIT Technology Review, and Morgan Stanley has predicted they could help double the value of the high-end computing market to reach $10 billion in the next decade. While a fully fledged quantum computer is yet to come, development over the past five years has been fast. The promise of such machines to massively outperform classical computers at some tasks makes quantum computing a potentially disruptive technology. Applications include quantum speed ups for artificial intelligence, finance modelling, drug design, and big data analysis. At this event, we will discuss the latest global developments, the position of Singapore in this new quantum world and the latest efforts by the quantum hardware lab at Google.
More information and registration: https://cqt.eventbrite.sg/
Title: What is quantum mechanics, and why? An insight from classical statistical mechanics with an ontic-nonseparability and an epistemic restriction.
Date/Time: 12-Apr, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: How does quantum randomness differ fundamentally from classical randomness? Where do they part ways? An answer could be of practical importance to better understand the physical resource and mechanisms underlying the superiority of quantum information protocols relative to their classical counterparts. In the talk, I show that (nonrelativistic) quantum mechanics (without spin) and classical statistical mechanics can be derived within a common axiomatic framework, imposing the principles of conservation of average energy. Relative to classical statistical mechanics, quantum mechanics is distinguished by two conceptual innovations: a) an "ontic extension" introducing an ontic-nonseparability via a global-nonseparable hypothetical ontic variable, fluctuating randomly with a strength on the order of Planck constant, and b) a specific "epistemic restriction" that it is no longer permitted to assign arbitrary weight to a trajectory independent of the underlying momentum field, yielding a constraint on the allowed phase space distribution. Quantum mechanics emerges from the model as we average over the fluctuations of the nonseparable variable. Specifically, the ontic extension and epistemic restriction are shown to imply quantum uncertainty and correlation. The talk will be based on our recent work: A. Budiyono and D. Rohrlich, Nature Communications 8, 1306 (2017).
Title: Quantum computers: how they work and what they'll mean for business
Date/Time: 29-Mar, 06:30PM
Venue: Impact Hub, Singapore, Level 1, 128 Prinsep Street
Abstract: Quantum computing was ranked as one of the top 10 breakthrough technologies in 2017 by MIT Technology Review, and Morgan Stanley has predicted they could help double the value of the high-end computing market to reach $10 billion in the next decade. While a fully fledged quantum computer is yet to come, development over the past five years has been fast. The promise of such machines to massively outperform classical computers at some tasks makes quantum computing a potentially disruptive technology. Applications include quantum speed ups for artificial intelligence, finance modelling, drug design, and big data analysis. At this event, we will discuss the latest global developments, the position of Singapore in this new quantum world and the latest efforts by the quantum hardware lab at Google. More information and registration: https://cqt.eventbrite.sg/
Title: Phonon-based systems and a quantum rotor in trapped ions for quantum information processing
Date/Time: 26-Apr, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: In the study of quantum information processing using trapped ions, phonons have been usually used as mediators of information, while they have useful properties in their own right for use as independent degrees of freedom. Phonons obey the Bose-Einstein statistics, and can take global as well as local characteristics by tuning trap parameters. These properties can be utilized for such areas as quantum simulation and quantum computation. In this talk I would like to present three topics related to experiments using phonons or motions in trapped ions. The first one is experiments on two-phonon interference and prospects toward realization of phonon-based information processing including boson sampling. The second topic is the quantum simulation of strongly interacting particles in solid-state materials based on polaritonic quasiparticles in trapped ions. Polaritonic quasiparticles, each of which is a superposition of an internal excitation and a phonon, are produced by illuminating red-sideband optical pulses to ions and are considered to be repulsively interacting with each other. The last topic is the study of a ''quantum rotor'' made from a three-ion crystal in a triangular shape. The superpositions of optically discernible two orientations are realized by cooling a rotational mode to its ground state and by applying a static magnetic field.
Title: General framework for the characterization of complex processes with memory
Date/Time: 05-Apr, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Traditional descriptions of the dynamics of open quantum systems are plagued by unphysical results as soon as memory effects play a non-negligible role. These effects commonly arise when the system of interest has a complex and structured environment. To make matters worse, the mere definition of a quantum stochastic process, as well as memory and memory effects in the quantum regime is still subject of active debate and not generally agreed upon. To remedy these shortcomings, a new unified scheme for operationally describing general quantum dynamics, known as the process tensor formalism, has been developed. This new framework allows -- independent of the details of the system-environment interaction -- for a full characterization of the underlying dynamics based on a finite number of local manipulations, and enables one to quantify its complexity in an unambiguous manner. In my talk, I will outline this general formalism, and illustrate how it naturally generalizes the theory of classical stochastic processes to the quantum regime, thus putting both theories on an equally sound mathematical footing. Furthermore, I will discuss, how this clear-cut understanding of general quantum processes elucidates the role of entanglement and memory effects as a resource for the simulation of processes that display exotic causal structures.
Title: Algorithms from Physics
Date/Time: 04-Apr, 03:30PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: In understanding physical systems over hundreds of years, Physicists have developed a wealth of dynamics and viewpoints. Some of these methods, when abstracted appropriately, could lead to new algorithmic techniques with applications to machine learning and TCS. I will present a couple of recent examples from my own research on such interactions between Physics and Algorithms -- a Hamiltonian Dynamics inspired algorithm for sampling from continuous distributions and a Boltzmann's equation based algorithm for counting discrete objects.
Title: Fairness and Diversity in Online Social Systems
Date/Time: 04-Apr, 02:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Social systems are now fueled by algorithms that facilitate and control connections and information. Simultaneously, computational systems are now fueled by people -- their interactions, data, and behavior. Consequently, there is a pressing need to design new algorithms that are socially responsible in how they learn, and socially optimal in the manner in which they use information. Recently, we have made initial progress in addressing such problems at this interface of social and computational systems. In this talk, we will first understand the emergence of bias in algorithmic decision making and present first steps towards developing a systematic framework to control biases in classical problems such as data summarization and personalization. This work leads to new algorithms that have the ability to alleviate bias and increase diversity while often simultaneously maintaining their theoretical or empirical performance with respect to the original metrics.
Title: Nonlinear Quantum Optics And Thermodynamics With Three Trapped Ions
Date/Time: 06-Apr, 11:00AM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: The trilinear interaction of bosonic modes, described by the Hamiltonian a^â€ bc + ab^â€ c^â€ , is a cornerstone in several branches of physics. In this talk, I will discuss the implementation of this trilinear interaction using three motional modes in a chain of three trapped ions. The coupling arises due to the anharmonicity of the Coulomb repulsion between ions and manifests itself at the level of single quanta. When combined with good control over the motional states and long coherence times afforded by the trapped ion system, it allows us to experimentally implement the quantum absorption refrigerator of thermodynamics, simulate the Jaynes-Cummings model of quantum optics, and even shed some light on the black-hole information paradox.
Title: Photonic Integrated Circuits for Scalable Addressing of Trapped Ion Systems
Date/Time: 13-Apr, 02:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: A key challenge in the realization of compact and scaled instruments based on trapped atomic ions is the optical system used for cooling, manipulation, and readout. We present current work using an integrated photonic approach for scaling trapped ion QIP systems, with results using 88Sr+. Nanometer-scale single mode waveguides are used to route light spanning the ultraviolet to NIR with low loss, and focusing vertical emission gratings create micron-size diffraction-limited spots at the trapping sites. Integrated detection schemes based on silicon avalanche photodetectors with custom high-speed quenching circuits are discussed. Early results from CMOS-fabricated traps with integrated APDs are presented, with a path toward high-speed integrated readout of single-ion fluorescence. Key fabrication issues, scaling challenges, and future work are outlined.
Title: Transport And Interaction of RB87 Atoms In A Dilution Fridge
Date/Time: 12-Apr, 03:00PM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: Superconducting qubits are capable of performing significantly faster computation compared to atomic qubits. However, the microseconds lifetime of the qubit is still significantly shorter compared to atomic states that could last up to seconds. By combining both superconducting and atomic systems, we can achieve fast computation in the superconducting qubits and stable storage in the atomic states. In our project, we aim to produce a strongly coupled atom-superconductor system that allows for fast state transfer from a superconducting qubit to an atomic state. Here, we describe the experimental setup involved in cloud generation, magnetic transport of the cloud over 70cm and the hardware behind our cryogenic system for the superconducting circuit. We have successfully transferred atoms to the fridge and expect N=1x108 87Rb atoms trapped near the mK cold plate. We plan for the trapping of the cloud to a superconducting 3D cavity to study its coupling strength. This will then pave the way for an actual state transfer from a superconducting qubit to the atoms.
Title: What quantum computing cannot do
Date/Time: 15-May, 06:30PM
Venue: Supply & Demande Esplanade - 8 Raffles Avenue, #01-13 Esplanade Mall
Abstract: In the popular press, quantum computers are often portrayed as being able to try all possible solutions to a problem at once. This is not the case, and the reality is much more subtle and interesting. We will see with an example that the real task in devising a quantum algorithm is to use interference (as when two water waves collide) to increase the probability of seeing good solutions and decrease the probability of seeing bad ones. Registration details: https://pintofsciencesg.wixsite.com/2018/atoms-to-galaxies-quantum-computing
Title: Quantum Technologies in Space
Date/Time: 16-May, 09:00AM
Venue: CQT Level 3 Seminar Room, S15-03-15
The aim of Quantum Technologies in Space workshop is to explore the intersection between space engineering and applicable technologies emerging from atomic and optical physics. Representatives from groups working in related fields are attending to summarise the progress of their experiments and discuss strategies for making them ready for space.
This workshop is organised by the team of Alexander Ling under the collaboration between National University of Singapore and Humboldt University of Berlin, Germany.
Title: Tradeoffs in Quantum Steering
Date/Time: 26-Apr, 11:00AM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Quantum steering was introduced by Schrodinger, in response to the famous paradox raised by Einstein, Podolsky, and Rosen (EPR) in 1935. It describes the conditioning effect between two parties, Alice and Bob say, that Bob's system could be remotely prepared into different states by different choices of Alice's measurements when they share a pure bipartite non-product state. In this talk, I will talk about the quantum steering for two-qubit states and beyond qubits. In particular, the following issues are examined: 1) Which states Bob's qubit can be steered to by Alice's qubit (qudit)? 2) What is the connection between this set of steered states and the degree of quantum correlation? 3) Which convex decomposition of Bob's local state can be steered to by Alice's qubit (qudit)? 4) And for a multi-party state, are there restrictions on the degree to which one party can steer the systems of all other parties? I will mainly use the quantum steering ellipsoid to tackle these problems and report monogamy relations of quantum steering ellipsoids for qubits systems and beyond qubits. This talk is largely based on my PhD thesis and relevant references are listed below: [1] Quantum steering ellipsoids (Phys. Rev. Lett. 113, 020402); [2] Monogamy of quantum steering ellipsoids (Phys. Rev. A 94, 042105); [3] Monogamy of EPR-steering ( Phys. Rev. Lett. 118, 010401).
Title: Talk & reception for visiting artist
Date/Time: 04-May, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Jun is a Kuala Lumpur-based architect and artist. His interest lies at the intersection of fine arts and applied arts in the context of South East Asia. He is currently obsessed with materiality - coupling low-tech materials with hi-tech application primarily with artificial light. Jun has previously worked at practices in Shanghai, Beijing & KL; most recently at the studio of British designer, Tom Dixon in London and has been featured in Hypebeast, Vice, Ignant & Designboom. He studied architecture at the University of Westminster in London and at the University of Melbourne. CQT is partnering with the ArtScience Museum to support Jun to develop an artwork inspired by quantum computing. The piece will be on display at the museum from October. Attend the talk to hear more from the artist about his work and from the museum team about the forthcoming exhibition - there will be opportunities for CQT members to participate as scientific advisors. There will be a tea reception after.
Title: On the power of conditional sampling: a special case of property testing
Date/Time: 25-Apr, 02:00PM
Venue: CQT Seminar Room, S15-03-15
Abstract: In the modern world of big data and fast computing, it is essential to design super fast algorithms. Often reading the whole data is either too costly or time-consuming and sometimes not feasible. Property testing is a subject that deals with these challenges. It tries to design sub-linear algorithms for testing various properties of inputs. The key lies in the way the data is accessed by the algorithm. One of the central problems in property testing and many other related subjects is testing if a distribution has a certain property - say whether a distribution on a finite set is uniform. The conventional way of accessing the distributions is by drawing samples according to the distributions. Unfortunately, in this setting the number of samples that are necessary for testing properties of distribution (for most natural properties) is polynomial in the size of support of the distribution. Thus when the support is relatively big the algorithms become impractical in real life applications. We define a new way of accessing the distribution using ``conditional-sampling oracle". This oracle can be used to design much faster algorithms for testing properties of distribution and thus makes the algorithm useful in practical scenarios. In fact we can show that any label-invariant property of distribution can be tested using constant number of conditional samples. In a couple of recent ongoing projects, we show that the conditional oracle can be implemented in many real life problems and we have been able to show the usefulness of this model and our algorithms in practical purposes and others areas of research. This model also throws a number of interesting theoretical questions.
Title: A second-quantized Shannon theory
Date/Time: 08-May, 02:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: In quantum Shannon theory, the way information is encoded and decoded takes advantage of the laws of quantum mechanics, while the way communication channels are interlinked is assumed to be classical. In this talk, I will relax the assumption that quantum channels are combined classically, and I will show that, in certain situations, combining quantum channels in an indefinite causal order allows us to achieve tasks that are impossible in conventional quantum Shannon theory. Specifically, I will show a phenomenon of causal activation, whereby two identical copies of a completely depolarizing channel become able to transmit information when they are combined in a quantum superposition of two alternative orders. This finding runs counter to the intuition that if two communication channels are identical, using them in different orders should not make any difference.
Title: Towards a maximal sensitivity matter-wave gyroscope
Date/Time: 09-May, 11:30AM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: We propose a method of atom interferometry using a spinor Bose-Einstein condensate with a time-varying magnetic field acting as a coherent beam splitter. Our protocol creates long-lived superpositional counterflow states, which are of fundamental interest and can be made sensitive to both the Sagnac effect and magnetic fields on the sub-μG scale. We split a ring-trapped condensate, initially in the mf=0 hyperfine state, into superpositions of internal mf=±1 states and condensate superflow, which are spin-orbit coupled. After interrogation, the relative phase accumulation can be inferred from a population transfer to the mf=±1 states. The counterflow generation protocol is adiabatically deterministic and does not rely on coupling to additional optical fields or mechanical stirring techniques. Our protocol can maximize the classical Fisher information for any rotation, magnetic field, or interrogation time and so has the maximum sensitivity available to uncorrelated particles. Precision can increase with the interrogation time and so is limited only by the lifetime of the condensate.
Title: Multi terminal hypothesis testing
Date/Time: 18-May, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: In the problem of Hypothesis testing, one has to decide between two alternative explanations for the data i.e Null Hypothesis $H_0$ and Alternate hypothesis $H_1$. We consider Multi-terminal Hypothesis testing when the data is distributed across two parties Alice and Bob under the restriction that Alice can communicate to Bob at a constant rate $R$. The goal is to characterize the set of possible type-2 error exponents as functions of the available communication rate so that the type-1 error probabilities is bounded by $\epsilon$. We study the problem in one-shot regime.
Title: Quantum Simplicity: A tour of complexity science in a quantum World
Date/Time: 21-Jun, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Complexity and quantum science appear at first to be two fields that bear little relation. One deals with the science of the very large â€“ seeking the understand how unexpected phenomena can emerge in vast systems consisting of many interacting components. Quantum theory, on the other hand, deals with particles at the microscopic level and is usually considered limited to the domain of individual photons and atoms. Yet, different as they appear, there is growing evidence that in interface ideas from quantum and complexity science, we may unveil new perspective in either both fields. In this presentation, I first introduce computational mechanics, a branch of complexity science captures structure by building the simplest causal models of natural observations. I then illustrate how many processes that require complex classical models may be simulated by remarkably simple quantum devices, and describe recent experiments to test this laboratory conditions. I then survey the potential consequences these developments to long-standing topics of interesting in both complexity and quantum science. The former in indicating that well-established notions of structure, complexity, may change when the quantum properties of information are taken into account. The latter in uncovering a new source of highlighting how a new source of temporal asymmetry can arise through classicalization. References: â€¢ Quantum mechanics can reduce the complexity of classical models, Nature Communications 3, 762 â€¢ Experimental quantum processing enhancement in modelling stochastic processes, Science Advances Vol. 3, no. 2, e160130. â€¢ Using quantum theory to simplify inputâ€“output processes. Nature partner journal: Quantum Information 3, 1 â€¢ A practical, unitary simulator for non-Markovian complex processes. arXiv:1709.02375 [To appear in Phys. Rev Lett] â€¢ Causal Asymmetry in a Quantum World. arXiv:1712.02368 [To appear in Physics. Rev. X]
Title: Characterising the behaviour of classical-quantum broadcast networks
Date/Time: 19-Jun, 03:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: The indistinguishability of quantum states and the no-cloning theorem give fundamental restrictions to broadcasting of classical information over quantum networks. In this presentation, we introduce a method for characterising the stochastic matrix of any classical-quantum broadcast network, assuming only the inner product information of the quantum code states. Our method can analyse a wide range of quantum communication protocols, including those that employ infinite-dimensional quantum states. As an application of our new toolbox, we use it to reveal novel results in multipartite quantum random access coding.
Title: CQT PhD Oral Defense by Goh Koon Tong
Date/Time: 25-Jun, 03:00PM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: Quantum theory predicts the existence of correlations that violate local realism. In this thesis, we look at this fact from the reverse angle ("device-independent approach"): given that such non-local correlations are observed, what can we know about the quantum resources being used? It had been known for several years that some correlations are fingerprints of specific quantum states: this kind of blind tomography has been called "self-testing". Here we prove that every pure bipartite entangled state possesses such fingerprints, highlighting that self-testing is a generic phenomenon. Self-testing is also used in the demonstration that a proposed connection between non-locality and uncertainty relations is an artefact of cherry-picking the expression of Bell inequality equivalent under no-signalling. Finally, we report the first comprehensive geometric study of the set of quantum correlations, bringing to the fore an unexpected complexity of features.
Title: Stories about the second law(s) of thermodynamics
Date/Time: 20-Jun, 11:00AM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: In this talk, I shall compare various versions of the second law of thermodynamics: in phenomenology, in the theory of open quantum systems applied to thermal machines, and in the resource theories of thermal operations. (This is a rehearsal for a talk in a conference, feedback is specially welcome).
Title: Production of ultracold ground state 6Li40K molecules and investigation by microwave spectroscopy
Date/Time: 09-Jul, 05:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: We study ultracold heteronuclear dimers of 6Li40K in their deeply-bound ro-vibronic states which possess a large electric dipole moment of 3.6 Debye. This makes them a suitable candidate for exhibiting strong effects of the long-range and anisotropic nature of the dipole-dipole interactions. Starting from a sympathetically cooled, quantum-degenerate Fermi-Fermi mixture, we create weakly-bound bosonic 6Li - 40K molecules and excite them to a single hyperfine state. We present two-photon spectroscopy to investigate the deeply-bound ro-vibrational levels of the electronic ground state of molecules. Our goal is to produce ultracold ground state dipolar molecules via Stimulated Raman Adiabatic Passage and apply a strong external electric field to induce dipole-dipole interactions. We want to investigate the microwave spectra of the molecular ground state, including hyperfine interactions in the presence of electric and magnetic fields. We will use microwaves to induce repulsive long-range interactions that shield molecular collisions.
Title: Light-atom Coupling with 4Pi Microscopy
Date/Time: 13-Jul, 10:00AM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: An efficient light-matter interface is foundational to the development of a distributed quantum network. In this defence, I present the experimental realisation of an interface by tightly focusing light onto single atoms with a pair of high numerical aperture (NA=0.75) lenses. Operating near the diffraction limit, the length scale of the light field approaches that of the thermal motion of trapped atoms. Therefore, I focus my study not only on the localisation of the light field but also of the atoms. Three core experiments: (1) polarization gradient cooling, (2) the effects of thermal motion, and (3) coupling with 4Pi microscopy will be discussed in the context of light-atom interaction.
Title: Ultrathin Optical Fibre Applications from Atomic Physics through Quantum Optics
Date/Time: 12-Jul, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Ultrathin optical fibres, with diameters on the order of the propagating light wavelength, have already proven their versatility across a variety of different areas, such as sensing, particle manipulation, cold atom physics, and as optical couplers. The intense evanescent field at the fibre waist is one of the main advantages offered by these systems as it allows us to achieve ultrahigh light intensities that may otherwise not be attainable in a standard laboratory. In this talk, I will present work conducted at OIST related to the fields of atomic physics and quantum optics. For example, we embed ultrathin fibres into a laser-cooled sample of rubidium atoms for studies related to Rydberg atom formation near a dielectric surface and to study degenerate and nondegenerate two-photon processes. In another example, I’ll discuss work on structured ultrathin fibres that combine a Bragg grating with a cavity for enhanced photon coupling from a quantum emitter. Overall, the versatility of these fibres for many different experimental platforms – particularly if one goes beyond the basic, single mode fibre design – will be promoted.
Title: Prototyping of a high-speed, time-of-flight, distance measuring device for formation flying satellites.
Date/Time: 24-Jul, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: There are a multitude of ways of measuring distance, however not all are suitable for space. This study is focused on distance measurement using time of flight (TOF) and more specifically on the development of a space-compatible receiver device that operates at distances, around 1km, where the recovered energy is very low. A MPPC (Multi-Pixel Photon Counter) was investigated and developed into a prototype receiver. Crosstalk and afterpulse phenomena related to the MPPC were observed, and the limits of the system were established. The results highlighted the importance of a neat design and the limitations related to internal noise (produced by the circuit and the sensor) and external noise (stray light). The conclusion of this work is the realisation of a supervisory circuit for the functional MPPC. Although the card correctly conditions the pulses of current emitted by the sensor, improvements can be made. One of the developments envisaged is the acquisition of the pulses by FPGA and the processing (as well as the communication) would be left to the microcontroller. The use of FPGA would also implement digital filters and / or algorithms to bring out, more easily, the useful impulses embedded in the noise.
Title: Efficient information propagation in Feed Forward Neural Network
Date/Time: 27-Jul, 03:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Machine Learning is redefining the very way we interact with machines; in particular, algorithm based on Deep Neural Networks (DNN) deliver record breaking performances on tasks such as image classification and speech recognition. Recently, DNN have been also used to let machines create new pieces of art, such as painting, music and writing, tasks considered to be of properly human nature. This Renaissance of DNN based AI is mostly due to increased computer power and GPU based machines that made the simple, but numerically heavy calculations underlying many DNN architectures feasible. Nevertheless, still little is understood from a fundamental, mathematical point of view as most ML model are guided by heuristics and unknown, uncontrolled approximations that lead to an unsystematic growth of the model complexity. In particular, the ML community tend to distinguish between two seemingly different approaches: Feed Forward (FF) and Energy based. The former is the most used but less understood one, while the latter can be related to popular models of statistical mechanics but found little practical applications. In this talk I will discuss a statistical mechanics model we recently proposed to link together these two seemingly different approaches via a simple variational principle that recasts FF networks in Hamiltonian form. We show that in this way it is easy to obtain several known results of FF networks, but also show some of the problematics related to the use of heuristic non-linear activations. In particular we show how the well known problem of vanishing gradients arises from a dimensional mismatch induced by the use of such activations. Our framework simply provide the solution to this problem by providing the correct activation, that we term ESP (Expected signal propagation). Finally, the standard ReLu activation arises as a limiting case of ESP, providing in this way the first formal derivation of this popular activation. We highlight the probabilistic nature of ESP and study the eigenvalue spectrum of the associated Hessian on classification tasks. We find that ESP allows for faster training and more consistent performances over a wide range of network architectures. This means that ESP trained FF networks are less prone to fine tuning of their topology. Several open problems in classical and quantum machine learning can be tackled by means of the tools introduced in the talk, I will try to discuss these open problems and possibly convince you to join me working on them!
Title: One-shot Protocols for Communication Over Quantum Networks: Achievability and Limitation
Date/Time: 20-Jul, 03:00PM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: This thesis studies the problems of source compression and channel coding in the one-shot entanglement-assisted quantum setting. The main contribution of the first part of the thesis is to systematically develop one-shot protocols for various quantum tasks, using two unified tools of `convex-split' and `position-based decoding'. Convex-split is used for the encoding operations and position-based decoding, which can also be viewed as a dual to the convex-split, is used for decoding operation. Our protocols and achievability results closely resemble the corresponding protocols and results in the classical case. Furthermore, position-based decoding gives near optimal one-shot results for the point to point channel. In the second part of the thesis, we exhibit some limitations on how well quantum messages can be compressed. We show that efficient classical schemes, such as the Huffman coding scheme, are not possible in the quantum domain. As a complementary result, we show an exponential separation between quantum communication complexity and quantum information complexity. This shows the existence of a hard to compress interactive quantum protocol.
Title: Ideal clocks - a convenient fiction
Date/Time: 21-Aug, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: No device built according to the rules of quantum field theory can measure proper time along its path. Highly accelerated quantum clocks experience the Unruh effect, which inevitably influences their time rate. This contradicts the concept of an ideal clock, whose rate should only depend on the instantaneous velocity and not acceleration.
Title: Towards a space-based quantum key distribution network: developing a miniaturised
entangled photon source for nanosatellites
Date/Time: 27-Jul, 03:00PM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: Quantum key distribution (QKD) based on entangled photon pairs offers provable security underpinned by quantum physics. Current QKD networks have distance limits due to loses and satellite technology can be used to extend this network. We propose an iterative and cost effective approach to this challenge using an emerging nanosatellite standard called CubeSat. The first step towards this direction is to demonstrate a miniaturised polarization entangled photon pair source that is compatible with the resource-limited CubeSat. This thesis discusses the engineering and instrumentation of such a source. The initial prototype of the source was tested on a weather balloon 37km in altitude. Subsequently, we have tested the revised prototype in two space missions (GomX-2 and Galassia-NUS). These results establish space heritage for the components used and provide insights to refine the design leading to a space qualified QKD source.
Title: Entanglement-based tests of quantum gravity using two massive particles
Date/Time: 02-Aug, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Existing proposals for quantum gravity share the same deep problem. Their predictions are extremely hard to test in practice. Quantum effects in the gravitational field are exceptionally small, unlike those in the electromagnetic field. The fundamental reason is that the gravitational coupling constant is about 43 orders of magnitude smaller than the fine structure constant, which governs light-matter interactions. In this seminar I shall discuss a number of recent proposals, which are based on a radically different, quantum-information-theoretic approach to witnessing non-classicality of the gravitational field. These proposals consist of two parts. The first is a general argument showing that any system (e.g. a field) capable of mediating entanglement between two quantum systems must itself be quantum. The second part is a proposed experimental scheme to detect the entanglement generated between two masses via gravitational interaction. By the argument presented in the first part, the degree of entanglement between the masses is an indirect witness of the quantisation of the field mediating the interaction. Remarkably, these proposals do not require any quantum control over gravity itself. They are also closer to realisation than other proposals, such as detecting gravitons or detecting quantum gravitational vacuum fluctuations.
Title: Fluctuation Theorem for Quantum Bipartite Systems
Date/Time: 07-Aug, 11:00AM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: This thesis studies the interplay between non-equilibrium thermodynamics and quantum information. I have demonstrated fundamental theorems which link quantum information and non-equilibrium thermodynamic quantities in a quantum bipartite system. I will explain the details of these theorems, such as fluctuation theorems and their corresponding thermodynamic equations. I will also present an experimental realization of the theorems.
Title: Information theoretic and algebraic techniques in theoretical computer science.
Date/Time: 10-Aug, 03:00PM
Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: This thesis can be divided into four independent parts. 1.We give a one-round entanglement assisted quantum compression protocol that allows Alice and Bob (players) to sample from a common distribution known only to Alice. We also provide a quantum analogue of the widely used classical correlated-sampling protocol. 2.We prove some lower bounds on the randomized query complexity of composed relations. 3.We show that the deterministic interpolation of sparse polynomials with integer coefficients in the Schubert basis can be done in polynomial time, given an oracle computing Schubert polynomials. Also, computing both skew Schubert and Schubert polynomials on non-negative integral points is in #P and VNP (algebraic complexity). 4.We give a new sieving procedure with a linear sieve, that significantly improves the running time of the algorithm for Shortest Vector Problem and Closest Vector Problem on lattices in infinity norm.
Title: Blind State Quantum Tomography
Date/Time: 10-Aug, 02:00PM
Venue: CQT Level 6 Seminar Room, S15-06-22
Abstract: In this talk I will present a method for characterizing quantum state in the case when it is inaccessible experimentally, but is coupled to another system over which we have control. This technique is then used to construct useful model of non-markovian noise for quantum channels.
Title: Quantum change point
Date/Time: 17-Aug, 03:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Changes are ubiquitous in nature. Identifying them is crucial for a number of applications in biology, medicine and social sciences. The detection of when a sudden changes happen, known as the change point problem, is an important task in statistics. Consider a source that emits a stream of identical quantum states, and after a mutation, emits a stream of another state. Identifying when the mutation happens, analogous to the change point problem, is known as the quantum change point problem. In this journal club session, I will review some recent works by Gael et al., trying to explain the quantum change point problem, present their analysis of offline and online detection of the change point, exactly identification of the change point and discuss the connection between the (quantum) change point problem and (quantum) machine learning.
References: 1. G Sentís, E Bagan, J Calsamiglia, G Chiribella, R Munoz-Tapia, Physical review letters 117 (15), 150502 (2016) 2. G Sentís, J Calsamiglia, R Munoz-Tapia, Physical review letters 119 (14), 140506 (2017)
Title: Introduction to artificial neural network and TensorFlow
Date/Time: 24-Aug, 03:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: In this tutorial, I will discuss following topics:
1. Neural network
2. Forward propagation and back propagation
3. What deep learning means?
4. Regularization techniques
5. Introduction to TensorFlow
Title: Learning a local Hamiltonian from local measurements
Date/Time: 08-Aug, 03:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: Recovering an unknown Hamiltonian from measurements is an increasingly important task for certification of noisy quantum devices and simulators. Recent works have succeeded in recovering the Hamiltonian of an isolated quantum system with local interactions from long-ranged correlators of a single eigenstate. Here we generalize these works to allow for the recovery of the Hamlitonian from any state that commutes with it, including, for example, the Gibbs state at a finite temperature. Our approach takes advantage of the non-commuteness of the underlying Hamiltonian to derive non-trivial local constraints between the local reduced density matrices and the local Hamiltonian terms. This enables us to learn a local patch of the Hamiltonian from local observations only on that patch, even though the overall state might be globally entangled. Surprisingly, in many relevant cases, our algorithm is exponentially faster than the classical problem of learning a Boltzmann machine, or, more generally, a graphical model. Based on the recent work with E. Bairey and N. Lindner, arXiv:1807.04564
Title: Efficient quantum information processing tasks with coherent state fingerprints
Date/Time: 13-Aug, 02:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: We provide the first example of a communication model and a distributed task, for which there exists a realistic quantum protocol that is asymptotically more efficient than any classical protocol, both in the communication and the information resources. For this, we extend a recently proposed coherent state mapping for quantum communication protocols, study the use of coherent state fingerprints over multiple channels and show their role in the design of an efficient quantum protocol for estimating the Euclidean distance of two real vectors within a constant factor. Further, we give a proposal on how to use this coherent state mapping for cryptographic tasks such as creating unforgeable quantum money with high noise tolerance.