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Supervised learning for quantum maximum entropy estimation

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arXiv 2020年

作者： Cao, Ningping Xie, Jie Zhang, Aonan Hou, Shi-Yao Zhang, Lijian Zeng, Bei Department of Mathematics & Statistics University of Guelph GuelphONN1G 2W1 Canada Institute for Quantum Computing University of Waterloo WaterlooONN2L 3G1 Canada National Laboratory of Solid State Microstructures College of Engineering and Applied Sciences School of Physics Nanjing University Nanjing210093 China Collaborative Innovation Center of Advanced Microstructures Nanjing University Nanjing210093 China College of Physics and Electronic Engineering Center for Computational Sciences Sichuan Normal University Chengdu610068 China Department of Physics Hong Kong University of Science and Technology Clear Water Bay Kowloon Hong Kong

For an unknown quantum state ρ, a set of measurement outcomes provides partial information. The principe of maximum entropy states that the density matrix which best represents the current knowlege is the one with the maximum entropy. However, the maximum entropy estimation (MEE) is hard to calculate in general. In this work, we develop a method that outputs an approximation to the MEE from limited measurement results by using supervised learning techniques. The method estimates the MEE of theoretical data of several different quantum systems with high fidelities. We also test our method experimentally with a photonic set-up, which exhibits high fidelities (all greater than 99.7%) and robustness against experimental errors. In comparison with previous known optimization algorithms for MEE, our method provides adequate fidelities with high efficiency. Copyright © 2020, The Authors. All rights reserved.

关键词： quantum optics

Thresholded quantum LIDAR – Exploiting photon-number-resolving detection

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arXiv 2019年

作者： Cohen, Lior Matekole, Elisha S. Sher, Yoni Istrati, Daniel Eisenberg, Hagai S. Dowling, Jonathan P. Hearne Institute for Theoretical Physics Department of Physics and Astronomy Louisiana State University Baton RougeLA70803 United States School of Computer Science and Engineering Hebrew University of Jerusalem Jerusalem91904 Israel Racah Institue for Physics Hebrew University of Jerusalem Jerusalem91904 Israel NYU-ECNU Institute of Physics at NYU Shanghai 3663 Zhongshan Road North Shanghai200062 China LCAS-Alibaba Quantum Computing Laboratory CAS Center for Excellence in Quantum Information and Quantum Physics University of Science and Technology of China Shanghai201315 China National Institute of Information and Communications Technology 4-2-1 Nukui-Kitamachi Koganei Tokyo184-8795 Japan

We present a technique that improves the signal-to-noise-ratio (SNR) of range-finding, sensing, and other light-detection applications. The technique filters out low photon numbers using photon-number-resolving detectors (PNRDs). This technique has no classical analog and cannot be done with classical detectors. We investigate the properties of our technique and show under what conditions the scheme surpasses the classical SNR. Finally, we simulate the operation of a rangefinder, showing improvement with a low number of signal samplings and confirming the theory with a high number of signal samplings. Copyright © 2019, The Authors. All rights reserved.

关键词： Signal to noise ratio

Multielemental single-atom-thick A layers in nanolaminated V2(Sn, A)C (A=Fe, Co, Ni, Mn) for tailoring magnetic properties

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arXiv 2019年

作者： Li, Youbing Lu, Jun Li, Mian Chang, Keke Zha, Xianhu Zhang, Yiming Chen, Ke Persson, Per O.Å. Hultman, Lars Eklund, Per Du, Shiyu Chai, Zhifang Huang, Zhengren Huang, Qing Engineering Laboratory of Advanced Energy Materials Ningbo Institute of Materials Technology and Engineering Chinese Academy of Sciences Ningbo Zhejiang315201 China University of Chinese Academy of Sciences 19 A Yuquan Rd Shijingshan District Beijing100049 China Linköping University LinköpingSE-581 83 Sweden Center for Quantum Computing Peng Cheng Laboratory Shenzhen518055 China

Tailoring of individual single-atom-thick layers in nanolaminated materials offers atomic-level control over material properties. Nonetheless, multielement alloying in individual atomic layers in nanolaminates is largely unexplored. Here, we report a series of inherently nanolaminated V2(A'xSn1-x)C (A'=Fe, Co, Ni and Mn, and combinations thereof, with x≈1/3) synthesized by an alloy-guided reaction. The simultaneous occupancy of the four magnetic elements and Sn, the individual single-atom-thick A layers in the compound constitute high-entropy-alloy analogues, two-dimensional in the sense that the alloying exclusively occurs in the A layers. V2(A'xSn1-x)C exhibit distinct ferromagnetic behavior that can be compositionally tailored from the multielement A-layer alloying. This two-dimensional alloying provides a structural-design route with expanded chemical space for discovering materials and exploit properties. Copyright © 2019, The Authors. All rights reserved.

关键词： Alloying

Advances in space quantum communications

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arXiv 2021年

作者： Sidhu, Jasminder S. Joshi, Siddarth K. Gündogan, Mustafa Brougham, Thomas Lowndes, David Mazzarella, Luca Krutzik, Markus Mohapatra, Sonali Dequal, Daniele Vallone, Giuseppe Villoresi, Paolo Ling, Alexander Jennewein, Thomas Mohageg, Makan Rarity, John Fuentes, Ivette Pirandola, Stefano Oi, Daniel K.L. SUPA Department of Physics University of Strathclyde 107 Rottenrow GlasgowG4 0NG United Kingdom Quantum Engineering Technology Labs H. H. Wills Physics Laboratory Department of Electrical and Electronic Engineering University of Bristol Merchant Venturers Building Woodland Road BristolBS8 1UB United Kingdom Institüt für Physik Humboldt-Universität zu Berlin Newtonstr. 15 Berlin12489 Germany Jet Propulsion Laboratory California Institute of Technology United States Scientific Research Unit Agenzia Spaziale Italiana Matera Italy Dipartimento di Ingegneria dell'Informazione Università degli Studi di Padova Padova35131 Italy Dipartimento di Fisica e Astronomia Università degli Studi di Padova Padova35131 Italy Centre for Quantum Technologies National University of Singapore S15-02-10 3 Science Drive 2 Singapore117543 Singapore Department of Physics 2 Science Drive 3 Blk S12 Level 2 Singapore117551 Singapore Institute for Quantum Computing University of Waterloo WaterlooONN2L 3G1 Canada Department of Physics and Astronomy University of Waterloo WaterlooONN2L 3G1 Canada School of Physics and Astronomy University of Southampton SouthamptonSO17 1BJ United Kingdom Department of Computer Science University of York YorkYO10 5GH United Kingdom Craft Prospect Ltd. Suite 4A Fairfield 1048 Govan Road GlasgowG51 4XS United Kingdom

Concerted efforts are underway to establish an infrastructure for a global quantum internet to realise a spectrum of quantum technologies. This will enable more precise sensors, secure communications, and faster data processing. quantum communications are a front-runner with quantum networks already implemented in several metropolitan areas. A number of recent proposals have modelled the use of space segments to overcome range limitations of purely terrestrial networks. Rapid progress in the design of quantum devices have enabled their deployment in space for in-orbit demonstrations. We review developments in this emerging area of space-based quantum technologies and provide a roadmap of key milestones towards a complete, global quantum networked landscape. Small satellites hold increasing promise to provide a cost effective coverage required to realised the quantum internet. We review the state of art in small satellite missions and collate the most current in-field demonstrations of quantum cryptography. We summarise important challenges in space quantum technologies that must be overcome and recent efforts to mitigate their effects. A perspective on future developments that would improve the performance of space quantum communications is included. We conclude with a discussion on fundamental physics experiments that could take advantage of a global, space-based quantum network. Copyright © 2021, The Authors. All rights reserved.

关键词： quantum cryptography

Bright-light detector control emulates the local bounds of Bell-type inequalities

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arXiv 2019年

作者： Sajeed, Shihan Sultana, Nigar Lim, Charles Ci Wen Makarov, Vadim Institute for Quantum Computing University of Waterloo WaterlooONN2L 3G1 Canada Department of Physics and Astronomy University of Waterloo WaterlooONN2L 3G1 Canada Department of Electrical and Computer Engineering University of Toronto M5S 3G4 Canada Centre for Quantum Technologies National University of Singapore Singapore Department of Electrical & Computer Engineering National University of Singapore Singapore Russian Quantum Center Skolkovo Moscow121205 Russia Shanghai Branch National Laboratory for Physical Sciences at Microscale CAS Center for Excellence in Quantum Information University of Science and Technology of China Shanghai201315 China NTI Center for Quantum Communications National University of Science and Technology MISiS Moscow119049 Russia

It is well-known that no local model—in theory—can simulate the outcome statistics of a Bell-type experiment as long as the detection efficiency is higher than a threshold value. For the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality this theoretical threshold value is ηT = 2(√2−1) ≈ 0.8284. On the other hand, Phys. Rev. Lett. 107, 170404 (2011) outlined an explicit practical model that can fake the CHSH inequality for a detection efficiency of up to 0.5. In this work, we close this gap. More specifically, we propose a method to emulate a Bell inequality at the threshold detection efficiency using existing optical detector control techniques. For a Clauser-Horne-Shimony-Holt inequality, it emulates the CHSH violation predicted by quantum mechanics up to ηT. For the Garg-Mermin inequality—re-calibrated by incorporating non-detection events—our method emulates its exact local bound at any efficiency above the threshold. This confirms that attacks on secure quantum communication protocols based on Bell violation is a real threat if the detection efficiency loophole is not closed. Copyright © 2019, The Authors. All rights reserved.

关键词： Bells

Tailoring magnetism in self-intercalated Cr1+δTe2 epitaxial films

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arXiv 2020年

作者： Fujisawa, Y. Pardo-Almanza, M. Garland, J. Yamagami, K. Zhu, X. Chen, X. Araki, K. Takeda, T. Kobayashi, M. Takeda, Y. Hsu, C.H. Chuang, F.C. Laskowski, R. Khoo, K.H. Soumyanarayanan, A. Okada, Yoshinori Okinawa904-0495 Japan Applied Physics & Mathematics Department Northeastern University BostonMA02115 United States Institute of Materials Research and Engineering Agency for Science Technology and Research Singapore138634 Singapore Department of Electrical Engineering and Information Systems University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo113-8656 Japan Center for Spintronics Research Network University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo113-8656 Japan Condensed Matter Science Division Quantum Beam Science Directorate Japan Atomic Energy Agency 1-1-1 Kouto Sayo-cho Sayo-gunHyogo679-5148 Japan Department of Physics National Sun Yat-sen University Kaohsiung80424 Taiwan Institute of High Performance Computing Agency for Science Technology and Research 138632 Singapore Department of Physics National University of Singapore 117551 Singapore

Magnetic transition metal dichalcogenide (TMD) films have recently emerged as promising candidates to host novel magnetic phases relevant to next-generation spintronic devices. However, systematic control of the magnetization orientation, or anisotropy, and its thermal stability, characterized by Curie temperature (Tc) – remains to be achieved in such films. Here we present self-intercalated epitaxial Cr1+δTe2 films as a platform for achieving systematic/smooth magnetic tailoring in TMD films. Using a molecular beam epitaxy (MBE) based technique, we have realized epitaxial Cr1+δTe2 films with smoothly tunable δ over a wide range (0.33-0.82), while maintaining NiAs-type crystal structure. With increasing δ, we found monotonic enhancement of Tc from 160 to 350 K, and the rotation of magnetic anisotropy from out-of-plane to in-plane easy axis configuration for fixed film thickness. Contributions from conventional dipolar and orbital moment terms are insufficient to explain the observed evolution of magnetic behavior with δ. Instead, ab initio calculations suggest that the emergence of antiferromagnetic interactions with δ, and its interplay with conventional ferromagnetism, may play a key role in the observed trends. To our knowledge, this constitutes the first demonstration of tunable Tc and magnetic anisotropy across room temperature in TMD films, and paves the way for engineering novel magnetic phases for spintronic applications. Copyright © 2020, The Authors. All rights reserved.

关键词： Transition metals

Joint Determination of Reactor Antineutrino Spectra from 235U and 239Pu Fission by Daya Bay and PROSPECT

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arXiv 2021年

作者： An, F.P. Andriamirado, M. Balantekin, A.B. Band, H.R. Bass, C.D. Bergeron, D.E. Berish, D. Bishai, M. Blyth, S. Bowden, N.S. Bryan, C.D. Cao, G.F. Cao, J. Chang, J.F. Chang, Y. Chen, H.S. Chen, S.M. Chen, Y. Chen, Y.X. Cheng, J. Cheng, Z.K. Cherwinka, J.J. Chu, M.C. Classen, T. Conant, A.J. Cummings, J.P. Dalager, O. Deichert, G. Delgado, A. Deng, F.S. Ding, Y.Y. Diwan, M.V. Dohnal, T. Dolinski, M.J. Dolzhikov, D. Dove, J. Dvořák, M. Dwyer, D.A. Erickson, A. Foust, B.T. Gaison, J.K. Galindo-Uribarri, A. Gallo, J.P. Gilbert, C.E. Gonchar, M. Gong, G.H. Gong, H. Grassi, M. Gu, W.Q. Guo, J.Y. Guo, L. Guo, X.H. Guo, Y.H. Guo, Z. Hackenburg, R.W. Hans, S. Hansell, A.B. He, M. Heeger, K.M. Heffron, B. Heng, Y.K. Hor, Y.K. Hsiung, Y.B. Hu, B.Z. Hu, Jianrun R. Hu, T. Hu, Z.J. Huang, H.X. Huang, J.H. Huang, X.T. Huang, Y.B. Huber, P. Koblanski, J. Jaffe, D.E. Jayakumar, S. Jen, K.L. Ji, X.L. Ji, X.P. Johnson, R.A. Jones, D.C. Kang, L. Kettell, S.H. Kohn, S. Kramer, M. Kyzylova, O. Lane, C.E. Langford, T.J. LaRosa, J. Lee, J.H.C. Lei, R.T. Leitner, R. Leung, J.K.C. Li, F. Li, H.L. Li, J.J. Li, Q.J. Li, R.H. Li, S. Li, S.C. Li, W.D. Li, X.N. Li, X.Q. Li, Y.F. Li, Z.B. Liang, H. Lin, C.J. Lin, G.L. Lin, S. Ling, J.J. Link, J.M. Littenberg, L. Littlejohn, B.R. Liu, J.C. Liu, J.L. Liu, J.X. Lu, C. Lu, H.Q. Lu, X. Luk, K.B. Ma, B.Z. Ma, X.B. Ma, X.Y. Ma, Y.Q. Mandujano, R.C. Maricic, J. Marshall, C. McDonald, K.T. McKeown, R.D. Mendenhall, M.P. Meng, Y. Meyer, A.M. Milincic, R. Mueller, P.E. Mumm, H.P. Napolitano, J. Naumov, D. Naumova, E. Neilson, R. Nguyen, T.M.T. Nikkel, J.A. Nour, S. Ochoa-Ricoux, J.P. Olshevskiy, A. Palomino, J.L. Pan, H.-R. Park, J. Patton, S. Peng, J.C. Pun, C.S.J. Pushin, D.A. Qi, F.Z. Qi, M. Qian, X. Raper, N. Ren, J. Morales Reveco, C. Rosero, R. Roskovec, B. Ruan, X.C. Searles, M. Steiner, H. Sun, J.L. Surukuchi, P.T. Tmej, T. Treskov, K. Institute of Modern Physics East China University of Science and Technology Shanghai China Department of Physics Illinois Institute of Technology ChicagoIL United States Department of Physics University of Wisconsin Madison MadisonWI United States Wright Laboratory Department of Physics Yale University New HavenCT United States Department of Physics Le Moyne College SyracuseNY United States National Institute of Standards and Technology GaithersburgMD United States Department of Physics Temple University PhiladelphiaPA United States Brookhaven National Laboratory UptonNY United States Department of Physics National Taiwan University Taipei Taiwan Nuclear and Chemical Sciences Division Lawrence Livermore National Laboratory LivermoreCA United States High Flux Isotope Reactor Oak Ridge National Laboratory Oak RidgeTN United States Institute of High Energy Physics Beijing China National United University Miao-Li Liechtenstein Department of Engineering Physics Tsinghua University Beijing China Shenzhen University Shenzhen China University Guangzhou China North China Electric Power University Beijing China Chinese University of Hong Kong Hong Kong Siena College LoudonvilleNY12211 United States Department of Physics and Astronomy University of California IrvineCA92697 United States Physics Division Oak Ridge National Laboratory Oak RidgeTN United States Department of Physics and Astronomy University of Tennessee KnoxvilleTN United States University of Science and Technology of China Hefei China Charles University Faculty of Mathematics and Physics Prague Czech Republic Department of Physics Drexel University PhiladelphiaPA United States Joint Institute for Nuclear Research Moscow Region Dubna Russia Department of Physics University of Illinois at Urbana-Champaign UrbanaIL61801 United States Lawrence Berkeley National Laboratory BerkeleyCA94720 United States George W. Woodruff School of Mechanical Engineering Georgia Institute

A joint determination of the reactor antineutrino spectra resulting from the fission of 235U and 239Pu has been carried out by the Daya Bay and PROSPECT collaborations. This Letter reports the level of consistency of 235U spectrum measurements from the two experiments and presents new results from a joint analysis of both data sets. The measurements are found to be consistent. The combined analysis reduces the degeneracy between the dominant 235U and 239Pu isotopes and improves the uncertainty of the 235U spectral shape to about 3%. The 235U and 239Pu antineutrino energy spectra are unfolded from the jointly deconvolved reactor spectra using the Wiener-SVD unfolding method, providing a data-based reference for other reactor antineutrino experiments and other applications. This is the first measurement of the 235U and 239Pu spectra based on the combination of experiments at low- and highly enriched uranium reactors. © 2021, CC BY.

关键词： Uncertainty analysis

Entanglement entropy, quantum fluctuations, and thermal entropy in topological phases

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arXiv 2019年

作者： Hu, Yuting Wan, Yidun State Key Laboratory of Surface Physics Fudan University Shanghai200433 China Department of Physics Center for Field Theory and Particle Physics Fudan University Shanghai200433 China Institute for Nanoelectronic Devices and Quantum Computing Fudan University Shanghai200433 China Department of Physics Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China CAS Key Laboratory of Microscale Magnetic Resonance Department of Modern Physics University of Science and Technology of China Hefei Anhui230026 China Collaborative Innovation Center of Advanced Microstructures Nanjing210093 China

Entanglement entropy in topologically ordered matter phases has been computed extensively using various methods. In this paper, we study the entanglement entropy of topological phases in two-spaces from a new perspective-the perspective of quasiparticle fluctuations. In this picture, the entanglement spectrum of a topologically ordered system is identified with the spectrum of quasiparticle fluctuations of the system, and the entanglement entropy measures the maximal quasiparticle fluctuations on the EB. As a consequence, entanglement entropy corresponds to the thermal entropy of the quasiparticles at infinite temperature on the entanglement boundary. We corroborates our results with explicit computation in the quantum double model with/without boundaries. We then systematically construct the reduced density matrices of the quantum double model on generic 2-surfaces with boundaries. Copyright © 2019, The Authors. All rights reserved.

关键词： Entropy

Efficient Verification of Pure quantum States in the Adversarial Scenario

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arXiv 2019年

作者： Zhu, Huangjun Hayashi, Masahito Department of Physics Center for Field Theory and Particle Physics Fudan University Shanghai200433 China State Key Laboratory of Surface Physics Fudan University Shanghai200433 China Institute for Nanoelectronic Devices and Quantum Computing Fudan University Shanghai200433 China Collaborative Innovation Center of Advanced Microstructures Nanjing210093 China Graduate School of Mathematics Nagoya University Nagoya464-8602 Japan Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China Centre for Quantum Technologies National University of Singapore 3 Science Drive 2 117542 Singapore

Efficient verification of pure quantum states in the adversarial scenario is crucial to many applications in quantum information processing, such as blind measurement-based quantum computation and quantum networks. However, little is known about this subject so far. Here we establish a general framework for verifying pure quantum states in the adversarial scenario and clarify the resource cost. Moreover, we propose a simple and general recipe to constructing efficient verification protocols for the adversarial scenario from protocols for the nonadversarial scenario. With this recipe, arbitrary pure states can be verified in the adversarial scenario with almost the same efficiency as in the nonadversarial scenario. Many important quantum states in quantum information processing can be verified in the adversarial scenario with unprecedented high efficiencies. Copyright © 2019, The Authors. All rights reserved.

关键词： quantum optics