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arXiv 2019年

作者： Liu, Shuanglong Xu, Yang Wang, Yun-Peng Chen, Yong P. Fry, James N. Cheng, Hai-Ping Department of Physics University of Florida GainesvilleFL32611 United States Quantum Theory Project University of Florida GainesvilleFL32611 United States Department of Physics and Astronomy Purdue University West LafayetteIN47907 United States School of Electrical and Computer Engineering Purdue University West LafayetteIN47907 United States Birck Nanotechnology Center Purdue University West LafayetteIN47907 United States Purdue Quantum Science and Engineering Institute Purdue University West LafayetteIN47907 United States Center for Molecular Magnetic Quantum Materials University of Florida GainesvilleFL32611 United States

Interfaces between two topological insulators are of fundamental interest in condensed matter physics. Inspired by experimental efforts, we study interfacial processes between two slabs of BiSbTeSe2 (BSTS) via first principles calculations. Topological surface states are absent for the BSTS interface at its equilibrium separation, but our calculations show that they appear if the inter-slab distance is greater than 6 Å. More importantly, we find that topological interface states can be preserved by inserting two or more layers of hexagonal boron nitride between the two BSTS slabs. Using a first-principles based method that allows us to simulate a back gate, we observe that the electric current tunneling through the interface is insensitive to back gate voltage when the bias voltage is small, in agreement with experimental observations. Analysis shows that at low bias the extra charge induced by a gate voltage resides on the surface that is closest to the gate electrode, leaving the interface almost undoped. This explains the origin of the observed insensitivity of transport properties to back voltage at low bias. Our study resolves a few questions raised in experiment, which does not yet offer a clear correlation between microscopic physics and transport data. We provide a road map for the design of vertical tunneling junctions involving the interface between two topological insulators. Copyright © 2019, The Authors. All rights reserved.

关键词： Electric insulators

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Laser damage attack against optical attenuators in quantum key distribution

arXiv

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arXiv 2019年

作者： Huang, Anqi Li, Ruoping Egorov, Vladimir Tchouragoulov, Serguei Kumar, Krtin Makarov, Vadim Institute for Quantum Information & State Key Laboratory of High Performance Computing College of Computer National University of Defense Technology Changsha410073 China Greatwall Quantum Laboratory China Greatwall Technology Changsha410205 China Institute for Quantum Computing University of Waterloo WaterlooONN2L 3G1 Canada Department of Electrical and Computer Engineering University of Waterloo WaterlooONN2L 3G1 Canada Department of Physics and Astronomy University of Waterloo WaterlooONN2L 3G1 Canada Faculty of Photonics and Optical Information ITMO University 199034 Kadetskaya line 3b St. Petersburg Russia QGLex Incorporated 105 Schneider Road Suite 111 OttawaONK2K 1Y3 Canada Russian Quantum Center Skolkovo Moscow143025 Russia Shanghai Branch National Laboratory for Physical Sciences at Microscale and 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

Many quantum key distribution systems employ a laser followed by an optical attenuator to prepare weak coherent states in the source. Their mean photon number must be pre-calibrated to guarantee the security of key distribution. Here we experimentally show that this calibration can be broken with a high-power laser attack. We have tested four fiber-optic attenuator types used in quantum key distribution systems, and found that two of them exhibit a permanent decrease in attenuation after laser damage. This results in higher mean photon numbers in the prepared states and may allow an eavesdropper to compromise the key. Copyright © 2019, The Authors. All rights reserved.

关键词： Photons

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A note on "quantum algorithm for linear systems of equations"

arXiv

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arXiv 2018年

作者： Xu, Yong-Zhen Huang, Yifan Ye, Zekun Li, Lvzhou Institute of Computer Science Theory School of Data and Computer Science Sun Yat-sen University Guangzhou510006 China Key Laboratory of Machine Intelligence and Advanced Computing Sun Yat-sen University Ministry of Education Guangzhou510006 China

Recently, an efficient quantum algorithm for linear systems of equations introduced by Harrow, Hassidim, and Lloyd, has received great concern from the academic community. However, the error and complexity analysis for this algorithm seems so complicated that it may not be applicable to other filter functions for other tasks. In this note, a concise proof is proposed. We hope that it may inspire some novel HHL-based algorithms that can compute F(A)|bi for any computable F. Copyright © 2018, The Authors. All rights reserved.

关键词： quantum theory

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Device-independent randomness expansion with entangled photons

arXiv

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arXiv 2019年

作者： Shalm, Lynden K. Zhang, Yanbao Bienfang, Joshua C. Schlager, Collin Stevens, Martin J. Mazurek, Michael D. Abellán, Carlos Amaya, Waldimar Mitchell, Morgan W. Alhejji, Mohammad A. Fu, Honghao Ornstein, Joel Mirin, Richard P. Nam, Sae Woo Knill, Emanuel Associate of the National Institute of Standards and Technology BoulderCO80305 United States Department of Physics University of Colorado BoulderCO United States NTT Basic Research Laboratories NTT Research Center for Theoretical Quantum Physics NTT Corporation 3-1 Morinosato-Wakamiya Atsugi Kanagawa243-0198 Japan National Institute of Standards and Technology GaithersburgMD20899 United States National Institute of Standards and Technology BoulderCO80305 United States JILA University of Colorado 440 UCB BoulderCO80309 United States 08860 Spain ICREA-Institució Catalana de Recerca i Estudis Avançats Barcelona08010 Spain Department of Computer Science Institute for Advanced Computer Studies Joint Center for Quantum Information and Computer Science University of Maryland College ParkMD20742 United States Department of Mathematics University of Colorado BoulderCO United States Center for Theory of Quantum Matter University of Colorado BoulderCO80309 United States

With the growing availability of experimental loophole-free Bell tests [1-5], it has become possible to implement a new class of device-independent random number generators whose output can be certified [6, 7] to be uniformly random without requiring a detailed model of the quantum devices used [8-10]. However, all of these experiments require many input bits in order to certify a small number of output bits, and it is an outstanding challenge to develop a system that generates more randomness than is used. Here, we devise a device-independent spot-checking protocol which uses only uniform bits as input. Implemented with a photonic loophole-free Bell test, we can produce 24% more certified output bits (1,181,264,237) than consumed input bits (953,301,640), which is 5 orders of magnitude more efficient than our previous work [10]. The experiment ran for 91.0 hours, creating randomness at an average rate of 3,606 bits/s with a soundness error bounded by 5.7×10−7 in the presence of classical side information. Our system will allow for greater trust in public sources of randomness, such as randomness beacons [11], and the protocols may one day enable high-quality sources of private randomness as the device footprint shrinks. Copyright © 2019, The Authors. All rights reserved.

关键词： Random processes

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Illinois Express quantum Network (IEQNET): Metropolitan-scale experimental quantum networking over deployed optical fiber

arXiv

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arXiv 2021年

作者： Chung, Joaquin Kanter, Gregory Lauk, Nikolai Valivarthi, Raju Wu, Wenji Ceballos, Russell R. Peña, Cristián Sinclair, Neil Thomas, Jordan Xie, Si Kettimuthu, Rajkumar Kumar, Prem Spentzouris, Panagiotis Spiropulu, Maria Data Science and Learning Division Argonne National Laboratory 9700 S Cass Ave. LemontIL60439 United States University of Chicago Consortium for Advanced Science and Engineering 924 E 57th St ChicagoIL60637 United States NuCrypt LLC 1840 Oak Ave EvanstonIL60201 United States Center for Photonic Communication and Computing Department of Electrical and Computer Engineering McCormick School of Engineering and Applied Science Northwestern University 2145 Sheridan Road EvanstonIL60208-3118 United States Division of Physics Mathematics and Astronomy California Institute of Technology 1200 E. California Blvd. PasadenaCA91125 United States California Institute of Technology 1200 E. California Blvd. PasadenaCA91125 United States Fermi National Accelerator Laboratory Kirk Rd and Pine St BataviaIL60510 United States Department of Chemistry Physics and Engineering Studies Chicago State University 9501 S. King Dr. ChicagoIL60628 United States Pittsburgh Quantum Institute B4 Thaw Hall 4061 O'Hara Street PittsburghPA15260 United States John A. Paulson School of Engineering and Applied Sciences Harvard University 29 Oxford St. CambridgeMA02138 United States 2205 Tech Drive Suite 1-160 EvanstonIL60208 United States Department of Physics and Astronomy Northwestern University 2145 Sheridan Road EvanstonIL60208-3112 United States

The Illinois Express quantum Network (IEQNET) is a program to realize metro-scale quantum networking over deployed optical fiber using currently available technology. IEQNET consists of multiple sites that are geographically dispersed in the Chicago metropolitan area. Each site has one or more quantum nodes (Q-nodes) representing the communication parties in a quantum network. Q-nodes generate or measure quantum signals such as entangled photons and communicate the results via standard, classical, means. The entangled photons in IEQNET nodes are generated at multiple wavelengths, and are selectively distributed to the desired users via optical switches. Here we describe the network architecture of IEQNET, including the Internet-inspired layered hierarchy that leverages software-defined-networking (SDN) technology to perform traditional wavelength routing and assignment between the Q-nodes. Specifically, SDN decouples the control and data planes, with the control plane being entirely classical. Issues associated with synchronization, calibration, network monitoring, and scheduling will be discussed. An important goal of IEQNET is demonstrating the extent to which the control plane can coexist with the data plane using the same fiber lines. This goal is furthered by the use of tunable narrow-band optical filtering at the receivers and, at least in some cases, a wide wavelength separation between the quantum and classical channels. We envision IEQNET to aid in developing robust and practical quantum networks by demonstrating metro-scale quantum communication tasks such as entanglement distribution and quantum-state teleportation. © 2021, CC BY.

关键词： Optical fibers

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Causal Limit on quantum Communication

引用

Physical Review Letters 2019年第15期123卷 150502-150502页

作者： Robert Pisarczyk Zhikuan Zhao Yingkai Ouyang Vlatko Vedral Joseph F. Fitzsimons Mathematical Institute University of Oxford Woodstock Road Oxford OX2 6GG United Kingdom Centre for Quantum Technologies National University of Singapore 3 Science Drive 2 117543 Singapore Department of Computer Science ETH Zürich Universitätstrasse 6 8092 Zürich Singapore University of Technology and Design 8 Somapah Road 487372 Singapore University of Sheffield Department of Physics and Astronomy 226 Hounsfield Rd Sheffield S3 7RH United Kingdom Clarendon Laboratory Department of Physics University of Oxford Parks Road Oxford OX1 3PU United Kingdom Department of Physics National University of Singapore 2 Science Drive 3 117542 Singapore Horizon Quantum Computing 79 Ayer Rajah Crescent Singapore 139955

The capacity of a channel is known to be equivalent to the highest rate at which it can generate entanglement. Analogous to entanglement, the notion of a causality measure characterizes the temporal aspect of quantum correlations. Despite holding an equally fundamental role in physics, temporal quantum correlations have yet to find their operational significance in quantum communication. Here we uncover a connection between quantum causality and channel capacity. We show the amount of temporal correlations between two ends of the noisy quantum channel, as quantified by a causality measure, implies a general upper bound on its channel capacity. The expression of this new bound is simpler to evaluate than most previously known bounds. We demonstrate the utility of this bound by applying it to a class of shifted depolarizing channels, which results in improvement over previously known bounds for this class of channels.

关键词： quantum channels quantum communication quantum foundations

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Symmetric versus bosonic extension for bipartite states

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Physical Review A 2019年第1期99卷 012332-012332页

作者： Youning Li Shilin Huang Dong Ruan Bei Zeng College of Science China Agricultural University Beijing 100080 People's Republic of China Department of Physics Tsinghua University Beijing 100084 People's Republic of China Collaborative Innovation Center of Quantum Matter Beijing 100190 People's Republic of China Institute for Interdisciplinary Information Sciences Tsinghua University Beijing 100084 People's Republic of China Department of Electrical and Computer Engineering Duke University Durham North Carolina 27708 USA Department of Mathematics & Statistics University of Guelph Guelph Ontario Canada N1G 2W1 Institute for Quantum Computing and Department of Physics and Astronomy University of Waterloo Waterloo Ontario Canada N2L 3G1

A bipartite state ρAB has a k-symmetric extension if there exists a (k+1)-partite state ρAB1B2...Bk with marginals ρABi=ρAB,∀i. The k-symmetric extension is called bosonic if ρAB1B2...Bk is supported on the symmetric subspace of B1B2...Bk. Understanding the structure of symmetric and bosonic extension has various applications in the theory of quantum entanglement, quantum key distribution, and the quantum marginal problem. In particular, bosonic extension gives a tighter bound for the quantum marginal problem based on separability. In general, it is known that a ρAB admitting symmetric extension may not have bosonic extension. In this work, we show that, when the dimension of the subsystem B is 2 (i.e., a qubit), ρAB admits a k-symmetric extension if and only if it has a k-bosonic extension. Our result has an immediate application to the quantum marginal problem and indicates a special structure for qubit systems based on group representation theory.

关键词： quantum correlations in quantum information quantum entanglement

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quantum black holes as solvents

arXiv

引用

arXiv 2019年

作者： Aurell, Erik Eckstein, Michal Horodecki, Pawel KTH Royal Institute of Technology AlbaNova University Center StockholmSE-106 91 Sweden Faculty of Physics Astronomy and Applied Computer Science Jagiellonian University Kraków30-348 Poland Institute of Theoretical Physics Jagiellonian University ul. Lojasiewicza 11 Kraków30-348 Poland Institute of Theoretical Physics and Astrophysics National Quantum Information Centre Faculty of Mathematics Physics and Informatics University of Gdansk Wita Stwosza 57 Gdansk80-308 Poland International Centre for Theory of Quantum Technologies Uniwersytet Gdanski Wita Stwosza 63 Gdansk80-308 Poland Faculty of Applied Physics and Mathematics National Quantum Information Centre Gdansk University of Technology Gabriela Narutowicza 11/12 Gdá nsk80-233 Poland

Almost all of the entropy in the universe is in the form of Bekenstein-Hawking (BH) entropy of super-massive black holes. This entropy, if it satisfies Boltzmann's equation S = log N, hence represents almost all the accessible phase space of the Universe, somehow associated to objects which themselves fill out a very small fraction of ordinary three-dimensional space. Although time scales are very long, it is believed that black holes will eventually evaporate by emitting Hawking radiation, which is thermal when counted mode by mode. A pure quantum state collapsing to a black hole will hence eventually re-emerge as a state with strictly positive entropy, which constitutes the famous black hole information paradox. Expanding on a remark by Hawking we posit that BH entropy is a thermodynamic entropy, which must be distinguished from information-theoretic entropy. The paradox can then be explained by information return in Hawking radiation. The novel perspective advanced here is that if BH entropy counts the number of accessible physical states in a quantum black hole, then the paradox can be seen as an instance of the fundamental problem of statistical mechanics. We suggest a specific analogy to the increase of the entropy in a solvation process. We further show that the huge phase volume (N), which must be made available to the universe in a gravitational collapse, cannot originate from the entanglement between ordinary matter and/or radiation inside and outside the black hole. We argue that, instead, the quantum degrees of freedom of the gravitational field must get activated near the singularity, resulting in a final state of the 'entangled entanglement' form involving both matter and gravity. Copyright © 2019, The Authors. All rights reserved.

关键词： quantum optics

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TensorFlow quantum: A software framework for quantum machine learning

arXiv

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arXiv 2020年

作者： Broughton, Michael Verdon, Guillaume McCourt, Trevor Martinez, Antonio J. Yoo, Jae Hyeon Isakov, Sergei V. Massey, Philip Halavati, Ramin Niu, Murphy Yuezhen Zlokapa, Alexander Peters, Evan Lockwood, Owen Skolik, Andrea Jerbi, Sofiene Dunjko, Vedran Leib, Martin Streif, Michael Von Dollen, David Chen, Hongxiang Cao, Shuxiang Wiersema, Roeland Huang, Hsin-Yuan McClean, Jarrod R. Babbush, Ryan Boixo, Sergio Bacon, Dave Ho, Alan K. Neven, Hartmut Mohseni, Masoud Google Quantum Ai Mountain ViewCA United States Sandbox Alphabet Mountain ViewCA United States Google Mountain ViewCA United States Institute for Quantum Computing University of Waterloo WaterlooONN2L 3G1 Canada School of Computer Science University of Waterloo WaterlooONN2L 3G1 Canada Department of Applied Mathematics University of Waterloo WaterlooONN2L 3G1 Canada Department of Mechanical and Mechatronics Engineering University of Waterloo WaterlooONN2L 3G1 Canada Department of Physics and Astronomy University of Waterloo WaterlooONN2L 3G1 Canada Division of Physics Mathematics and Astronomy Caltech PasadenaCA91125 United States Fermi National Accelerator Laboratory P.O. Box 500 BataviaIL605010 United States Department of Computer Science Rensselaer Polytechnic Institute TroyNY12180 United States Data:Lab Volkswagen Group Ungererstr. 69 München80805 Germany Leiden University Niels Bohrweg 1 Leiden2333 CA Netherlands Institute for Theoretical Physics University of Innsbruck Technikerstr. 21a InnsbruckA-6020 Austria Institute of Theoretical Physics Staudtstr. 7 Erlangen91058 Germany Volkswagen Group Advanced Technologies San FranciscoCA94108 United States Rahko Ltd. Finsbury Park LondonN4 3JP United Kingdom Department of Computer Science University College London WC1E 6BT United Kingdom Clarendon Laboratory Department of Physics University of Oxford OxfordOX1 3PU United Kingdom Vector Institute MaRS Centre TorontoONM5G 1M1 Canada Department of Physics and Astronomy University of Waterloo ONN2L 3G1 Canada Institute for Quantum Information and Matter Caltech PasadenaCA United States Department of Computing and Mathematical Sciences Caltech PasadenaCA United States

We introduce TensorFlow quantum (TFQ), an open source library for the rapid prototyping of hybrid quantum-classical models for classical or quantum data. This framework offers high-level abstractions for the design and training of both discriminative and generative quantum models under TensorFlow and supports high-performance quantum circuit simulators. We provide an overview of the software architecture and building blocks through several examples and review the theory of hybrid quantum-classical neural networks. We illustrate TFQ functionalities via several basic applications including supervised learning for quantum classification, quantum control, simulating noisy quantum circuits, and quantum approximate optimization. Moreover, we demonstrate how one can apply TFQ to tackle advanced quantum learning tasks including meta-learning, layerwise learning, Hamiltonian learning, sampling thermal states, variational quantum eigensolvers, classification of quantum phase transitions, generative adversarial networks, and reinforcement learning. We hope this framework provides the necessary tools for the quantum computing and machine learning research communities to explore models of both natural and artificial quantum systems, and ultimately discover new quantum algorithms which could potentially yield a quantum advantage. Copyright © 2020, The Authors. All rights reserved.

关键词： Open source software

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Benchmarking treewidth as a practical component of tensor-network–based quantum simulation

arXiv

引用

arXiv 2018年

作者： Dumitrescu, Eugene F. Fisher, Allison L. Goodrich, Timothy D. Humble, Travis S. Sullivan, Blair D. Wrigh, Andrew L. Quantum Computing Institute Oak Ridge National Laboratory Oak RidgeTN United States Department of Computer Science North Carolina State University RaleighNC United States

Tensor networks are powerful factorization techniques which reduce resource requirements for numerically simulating principal quantum many-body systems and algorithms. The computational complexity of a tensor network simulation depends on the tensor ranks and the order in which they are contracted. Unfortunately, computing optimal contraction sequences (orderings) in general is known to be a computationally difficult (NP-complete) task. In 2005, Markov and Shi showed that optimal contraction sequences correspond to optimal (minimum width) tree decompositions of a tensor network’s line graph, relating the contraction sequence problem to a rich literature in structural graph theory. While treewidth-based methods have largely been ignored in favor of dataset-specific algorithms in the prior tensor networks literature, we demonstrate their practical relevance for problems arising from two distinct methods used in quantum simulation: multi-scale entanglement renormalization ansatz (MERA) datasets and quantum circuits generated by the quantum approximate optimization algorithm (QAOA). We exhibit multiple regimes where treewidth-based algorithms outperform domain-specific algorithms, while demonstrating that the optimal choice of algorithm has a complex dependence on the network density, expected contraction complexity, and user run time requirements. We further provide an open source software framework designed with an emphasis on accessibility and extendability, enabling replicable experimental evaluations and future exploration of competing methods by practitioners. Copyright © 2018, The Authors. All rights reserved.

关键词： Tensors

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