## January 2020 | ||||||
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1 | 2 | 3 - CA2DM Seminar by Tianxing Ma, Beijing Normal University
**CA2DM Seminar by Tianxing Ma, Beijing Normal University**January 3, 2020 11:00 am - 12:00 pm CA2DM Theory Commons (S16, 06)Venue:CA2DM Theory Commons (S16, 06) Host:Shaffique Adam Title: Magnetic and superconductingcorrelation in monolayer and twisted bilayer graphene Abstract: Using exact quantum Monte Carlomethod, we identify the phase diagram of the half filled, the lightly doped andheavily doped graphene, which shows a rather rich physical properties. At halffilling, the system is driven to a Mott insulator with antiferromagnetic longrange order by increasing interaction, and a transition from a d+id pairing toa p+ip pairing is revealed, depends on the next-nearest hoping and theelectronic fillings. We also examine the recent novel electronic states seen inmagic-angle graphene superlattices. From the Hubbard model on a double-layerhoneycomb lattice with a rotation angle θ=1.08, we reveal that anantiferromagnetically ordered Mott insulator emerges beyond a critical Uc at half filling, and with a small doping, the pairing with d+id symmetrydominates over other pairings at low temperature. The effective d+id pairing interaction strongly increase as the on-site Coulomb interactionincreases, indicating that the superconductivity is driven by electron-electroncorrelation. Our non-biased numerical results demonstrate that the twistedbilayer graphene share the similar superconducting mechanism of hightemperature superconductors, which is a new and idea platform for furtherinvestigating the strongly correlated phenomena. **References**[1] Wanying Chen, Yonghuan Chu, Tongyun Huang, **TianxingMa***, arXiv:1903.01701.[2] Tongyun Huang, Lufeng Zhang, **Tianxing Ma***,Science Bulletin**64**, 310(2019).[3] **TianxingMa**, Lufeng Zhang, Chia-Chen Chang, Hsiang-Hsuan Hung, andRichard T. Scalettar, Phys. Rev. Lett.**120**, 116601(2018).[4] **Tianxing Ma,**Fan Yang, Hong Yao, Hai-Qing Lin, Phys. Rev. B**90**,245114 (2014).[5] **Tianxing Ma**, Zhongbing Huang, Feiming Hu andHai-Qing Lin, Phys. Rev. B**84**, 121410 (R) (2011).
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6 | 7 | 8 | 9 - CQT Colloquium by Konrad Banaszek, Centre for Quantum Optical Technologies and Faculty of Physics, University of Warsaw, Poland
**CQT Colloquium by Konrad Banaszek, Centre for Quantum Optical Technologies and Faculty of Physics, University of Warsaw, Poland**January 9, 2020 4:00 pm - 6:00 pm CQT Level 3 Seminar Room, S15-03-15Venue: CQT Level 3 Seminar Room, S15-03-15 Title: From quantum information science to deep-space optical communication Abstract: Quantum theory of electromagnetic radiation sets fundamental limits on the information capacity of optical communication links. Analysis of quantum mechanical capacity limits, which follow from Holevo's theorem, requires a change of paradigm from identifying noise inherent to measuring quantities well defined in classical systems, such as the amplitude or the phase of an optical field, to optimizing distinguishability of non-orthogonal quantum states. We discuss capacity limits in the context of deep-space optical communication, in particular downlink transfer of data collected by missions beyond the near-Earth region. The current standard for deep-space links is based on the high-order pulse position modulation (PPM) format. Such a format requires high peak-to-average power ratio of the optical signal, which may reduce the overall wall-plug efficiency of the transmitter subsystem. We describe a possible solution to this problem motivated by the quantum mechanical phenomenon of superadditivity of accessible information in classical communication.
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13 | 14 | 15 - CQT CS Talk by Debbie Lim
**CQT CS Talk by Debbie Lim**January 15, 2020 2:00 pm - 4:00 pm
Venue: CQT Level 3 Seminar Room, S15-03-15 Title: The aBc Problem and Equator Sampling for Rényi DivergencesAbstract: We investigate the problem of approximating the product aTBc, where a, c ∈ Sn−1 and B ∈ On, in models of communication complexity and streaming algorithms. The worst meaningful approximation is to simply decide whether the product is 1 or -1, given the promise that it is either. We call that problem the aBc problem. This is a modification of computing approximate inner products, by allowing a basis change. While very efficient streaming algorithms and one-way communication protocols are known for simple inner products (approximating aT c) we show that no efficient one-way protocols/streaming algorithms exist for the aBc problem. In communication complexity we consider the 3-player number-in-handmodel. We consider a setting where the players holding B, c may confer over many rounds, while there is only one message to Alice. Our main tools for lower bounds are geometric concentration results about R´enyi divergences. We show that: 1. In communication complexity aTBc can be approximated within additive error ǫ with communication O(√n/ǫ2) by a one-way protocol Charlie to Bob to Alice. 2. The aBc problem has a streaming algorithm that uses space O(√n log n) 3. Any one-way communication protocol for aBc needs communication at least (n1/3), and we prove a tight results regarding a communication tradeoff: if Charlie and Bob communicate over many rounds such that Charlie communicates o(n2/3) and Bob o(n1/3), and then the transcript is sent to Alice, the error will be large. 4. To establish our lower bound we show concentration results for R´enyi divergences under the event of restricting a density function on the sphere to a random equator and subsequently normalizing the restricted density function. This extends previous results by Klartag and Regev [6] for set sizes to R´enyi divergences of arbitrary density functions. 5. We show a strong concentration result for conditional R´enyi divergences on bipartite systems for all α > 1, which does not hold for α = 1. - NTU-PAP Colloquium by Guglielmo M. Tino, University of Florence
**NTU-PAP Colloquium by Guglielmo M. Tino, University of Florence**January 15, 2020 4:00 pm - 5:00 pm SPMS-LT3 (SPMS-03-02)Venue: SPMS-LT3 (SPMS-03-02) Title: Testing Gravity with Cold Atoms Abstract: The ability to control the quantum degrees of freedom of atoms using laser light opened the way to precision measurements of fundamental physical quantities. I will describe experiments for precision tests of gravitational physics using new quantum devices based on ultracold atoms, namely, atom interferometers and optical clocks. I will report on the measurement of the gravitational constant G with a Rb Raman interferometer, on experiments based on Bloch oscillations of Sr atoms confined in an optical lattice for gravity measurements at small spatial scales, and on new tests of the Einstein equivalence principle. I will also discuss prospects to use atoms as new detectors for gravitational waves and for experiments in space. Speaker Bio: Guglielmo Tino received the PhD in Physics in 1992 at the Scuola Normale Superiore of Pisa.Since 2001 he is Full Professor of Physics of Matter at the University of Florence. He was first Researcher and then Associate Professor at the University of Naples Federico II. In Florence, he started a new research group with four new laboratories for which he is responsible at the Department of Physics and INFN Section and the LENS Laboratory. He obtained funding for research projects from MIUR, INFN, EC, INFM, ASI, ESA, INGV, ENI, Tuscany Region, Ente Cassa di Risparmio di Firenze as national and international PI. Several R&D projects have been carried out with partners and industrial financing. In 2015 he founded the start-up AtomSensors s.r.l., Spin-off of the University of Florence.
• • | 16 - CQT Symposium by international and local speakers
**CQT Symposium by international and local speakers**January 16, 2020 2:00 pm - 8:00 pm SFAH Auditorium, Level 2, Shaw Foundation Alumni HouseVenue: SFAH Auditorium, Level 2, Shaw Foundation Alumni House Title: 12th Annual Symposium of the Centre for Quantum Technologies (CQT), Singapore Abstract: On the occasion of CQT's 12th anniversary, we invite you to join us for a symposium on quantum technologies with strong international and local speakers. We welcome all interested researchers and industry colleagues to the event on 16 January 2020. Registration is free.CQT was established in December 2007 as a national Research Centre of Excellence. It brings together physicists, computer scientists and engineers to do basic research on quantum physics and to build devices based on quantum phenomena. CQT's annual symposia provide an opportunity to discuss hot topics aligned with the Centre's research. These research directions span atomic, molecular and optical physics, quantum information, quantum foundations and computer science. Visit event website for program and details: https://cqt12.quantumlah.org/
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20 | 21 - Public Lecture Series at World Scientific- 9th Public Lecture by Leong Chuan Kwek
**Public Lecture Series at World Scientific- 9th Public Lecture by Leong Chuan Kwek**January 21, 2020 3:30 pm - 5:00 pm
Venue: World Scientific Publishing, Green Room, Level 1, 5 Toh Tuck Link, Singapore 596224 Title: Quantum Science and Technologies Abstract: There has been tremendous advancement in quantum science and technologies in recent years. Much of the hype has been attribute to the successess of quantum communication and huge investment in industry on quantum computers. However quantum science and technologies is not just restricted to quantum computing and communications. In this talk, I will provide landscape about the recent advances in quantum science and technologies.Free Admission. For registration, please email Amirova Nargiza, anargiza@wspc.com
• | 22 | 23 - CQT PhD QE II Presentation by Kapshikar Upendra Shamrao
**CQT PhD QE II Presentation by Kapshikar Upendra Shamrao**January 23, 2020 4:30 pm - 6:00 pm CQT Level 3 Seminar Room, S15-03-15Venue: CQT Level 3 Seminar Room, S15-03-15 Title: Code based cryptosystems, hidden subgroup problem and quantum Fourier sampling Abstract: McEliece and Niederreiter cryptosystems are robust and versatile cryptosystems. They are very popular these days as a potential candidate for post quantum cryptosystems. In this talk, we look at Niederreiter cryptosystems over quasi-cyclic codes and study their resistance to quantum Fourier sampling based attacks. We give a criterion for such cryptosystems to be resistance to quantum Fourier sampling and finally using classification of finite simple groups we show that QCC Niederreiter, for a large sized class, is resistant to hidden subgroup like attack.
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27 | 28 | 29 | 30 - CQT Talk by Marc Olivier Renou, University of Geneva, Genève (UNIGE)
**CQT Talk by Marc Olivier Renou, University of Geneva, Genève (UNIGE)**January 30, 2020 2:00 pm - 3:00 pm CQT Level 3 Seminar Room, S15-03-15Venue: CQT Level 3 Seminar Room, S15-03-15 Title: Genuine quantum triangle nonlocality and quantum Finnerinequality Abstract: Network nonlocality extends standard Bell nonlocality tonetworks, where several independent sources are distributed to several partiesaccording to the network structure. Contrary to standard Bell Nonlocality, thisproblem is non convex: no efficient systematic way to tackle it is known,either for local or quantum correlations. It is only partially understood forthe simplest scenarios of bilocality (extended to star-locality and nonlocalityon a line). However, for scenarios with loops, e.g. the triangle network,nothing is known except examples directly deduced from the usual form ofquantum nonlocality (via the violation of a standard Bell inequality). This caneven be done without using inputs. The question of finding a genuine quantumviolation of triangle network locality was open the last years. Inthis talk, we first present a novel example of quantum nonlocality withoutinputs in the triangle network, which we believe represent a new form ofquantum nonlocality, genuine to the triangle network. It involves bothentangled qubit states and joint entangled measurements. We generalize it toqutrits shared states and any odd-cycle networks. Then,we move to the question of the characterization of local and quantumcorrelations. We derive a bound, the quantum Finner inequality (already knownto hold for local ressources), which we also demonstrate to hold when thesources are arbitrary no-signaling boxes which can be wired together. Wegeneralizes this bound to all networks involving bipartite sources. We discussit as an application for the device-independent characterization of thetopology of a quantum network. Weconclude with some open questions related to quantum network nonlocality. Thistalk is based on arXiv:1905.04902 andarXiv:1901.08287
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