检索结果-内蒙古大学图书馆

Asymmetric particle transport and light-cone dynamics induced by anyonic statistics

学校读者我要写书评

暂无评论

arXiv 2018年

作者： Liu, Fangli Garrison, James R. Deng, Dong-Ling Gong, Zhe-Xuan Gorshkov, Alexey V. Joint Quantum Institute NIST/University of Maryland College ParkMD20742 United States Joint Center for Quantum Information and Computer Science NIST/University of Maryland College ParkMD20742 United States Center for Quantum Information IIIS Tsinghua University Beijing100084 China Condensed Matter Theory Center Department of Physics University of Maryland College ParkMD20742 United States Department of Physics Colorado School of Mines GoldenCO80401 United States

We study the non-equilibrium dynamics of Abelian anyons in a one-dimensional system. We find that the interplay of anyonic statistics and interactions gives rise to spatially asymmetric particle transport together with a novel dynamical symmetry that depends on the anyonic statistical angle and the sign of interactions. Moreover, we show that anyonic statistics induces asymmetric spreading of quantum information, characterized by asymmetric light cones of out-of-time-ordered correlators. Such asymmetric dynamics is in sharp contrast with the dynamics of conventional fermions or bosons, where both the transport and information dynamics are spatially symmetric. We further discuss experiments with cold atoms where the predicted phenomena can be observed using state-of-the-art technologies. Our results pave the way toward experimentally probing anyonic statistics through non-equilibrium dynamics. Copyright © 2018, The Authors. All rights reserved.

关键词： Statistics

ON THE EXISTENCE AND UNIQUENESS OF THE SOLUTION OF A PARABOLIC OPTIMAL CONTROL PROBLEM WITH UNCERTAIN INPUTS

学校读者我要写书评

暂无评论

arXiv 2018年

作者： Benner, Peter Onwunta, Akwum Stoll, Martin Computational Methods in Systems and Control Theory Max Planck Institute for Dynamics of Complex Technical Systems Sandtorstrasse 1 Magdeburg39106 Germany Department of Computer Science University of Maryland College ParkMD20742 United States Technische Universität Chemnitz Faculty of Mathematics Professorship Scientific Computing Chemnitz09107 Germany

In this note, we consider the existence and uniqueness of the solution of a time-dependent optimal control problem constrained by a partial differential equation with uncertain inputs. Relying on the Lions’ Lemma for deterministic problems, we furthermore characterize the optimal control of the stochastic problem. Copyright © 2018, The Authors. All rights reserved.

关键词： Optimal control systems

Fluctuation-induced torque on a topological insulator out of thermal equilibrium

学校读者我要写书评

暂无评论

arXiv 2018年

作者： Maghrebi, M.F. Gorshkov, A.V. Sau, J.D. Department of Physics and Astronomy Michigan State University East LansingMI48824 United States Joint Quantum Institute NIST/University of Maryland College ParkMD20742 United States Joint Center for Quantum Information and Computer Science NIST/University of Maryland College ParkMD20742 United States Condensed Matter Theory Center Physics Department University of Maryland College ParkMD20742 United States

Topological insulators with the time reversal symmetry broken exhibit strong magnetoelectric and magneto-optic effects. While these effects are well-understood in or near equilibrium, nonequilibrium physics is richer yet less explored. We consider a topological insulator thin film, weakly coupled to a ferromagnet, out of thermal equilibrium with a cold environment (quantum electrodynamics vacuum). We show that the heat flow to the environment is strongly circularly polarized, thus carrying away angular momentum and exerting a purely fluctuation-driven torque on the topological insulator film. Utilizing the Keldysh framework, we investigate the universal nonequilibrium response of the TI to the temperature difference with the environment. Finally, we argue that experimental observation of this effect is within reach. Copyright © 2018, The Authors. All rights reserved.

关键词： Thermodynamics

Symmetric vs. bosonic extension for bipartite states

学校读者我要写书评

暂无评论

arXiv 2018年

作者： Li, Youning Huang, Shilin Ruan, Dong Zeng, Bei College of Science China Agricultural University Beijing100080 China Department of Physics Tsinghua University Beijing China Collaborative Innovation Center of Quantum Matter Beijing100190 China Institute for Interdisciplinary Information Sciences Tsinghua University Beijing China Department of Electrical and Computer Enginnering Duke University DurhamNC27708 United States Department of Mathematics & Statistics University of Guelph GuelphON Canada Institute for Quantum Computing Department of Physics and Astronomy University of Waterloo WaterlooON Canada

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/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 seperability. 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. Copyright © 2018, The Authors. All rights reserved.

关键词： Bosons

Product spectrum Ansatz and the simplicity of thermal states

学校读者我要写书评

暂无评论

arXiv 2018年

作者： Martyn, John Swingle, Brian Department of Physics University of Maryland College ParkMD20742 United States Condensed Matter Theory Center Maryland Center for Fundamental Physics Joint Center for Quantum Information and Computer Science Department of Physics University of Maryland College ParkMD20742 United States Institute for Advanced Study PrincetonNJ08540 United States

Calculating the physical properties of quantum thermal states is a difficult problem for classical computers, rendering it intractable for most quantum many-body systems. A quantum computer, by contrast, would make many of these calculations feasible in principle, but it is still non-trivial to prepare a given thermal state or sample from it. It is also not known how to prepare special simple purifications of thermal states known as thermofield doubles, which play an important role in quantum many-body physics and quantum gravity. To address this problem, we propose a variational scheme to prepare approximate thermal states on a quantum computer by applying a series of two-qubit gates to a product mixed state. We apply our method to a non-integrable region of the mixed field Ising chain and the Sachdev-Ye-Kitaev model. We also demonstrate how our method can be easily extended to large systems governed by local Hamiltonians and the preparation of thermofield double states. By comparing our results with exact solutions, we find that our construction enables the efficient preparation of approximate thermal states on quantum devices. Our results can be interpreted as implying that the details of the many-body energy spectrum are not needed to capture simple thermal observables. Copyright © 2018, The Authors. All rights reserved.

关键词： Qubits

quantum Error Correction Decoheres Noise

学校读者我要写书评

暂无评论

Physical Review Letters 2018年第19期121卷 190501-190501页

作者： Stefanie J. Beale Joel J. Wallman Mauricio Gutiérrez Kenneth R. Brown Raymond Laflamme Institute for Quantum Computing and Department of Physics and Astronomy University of Waterloo Waterloo Ontario N2L 3G1 Canada Institute for Quantum Computing and Department of Applied Mathematics University of Waterloo Waterloo Ontario N2L 3G1 Canada Department of Physics College of Science Swansea University Singleton Park Swansea SA2 8PP United Kingdom Escuela de Química Universidad de Costa Rica San José 2060 Costa Rica Department of Electrical and Computer Engineering Chemistry and Physics Duke University Durham North Carolina 27708 USA Perimeter Institute for Theoretical Physics Waterloo N2L 2Y5 Ontario Canada

Typical studies of quantum error correction assume probabilistic Pauli noise, largely because it is relatively easy to analyze and simulate. Consequently, the effective logical noise due to physically realistic coherent errors is relatively unknown. Here, we prove that encoding a system in a stabilizer code and measuring error syndromes decoheres errors, that is, causes coherent errors to converge toward probabilistic Pauli errors, even when no recovery operations are applied. Two practical consequences are that the error rate in a logical circuit is well quantified by the average gate fidelity at the logical level and that essentially optimal recovery operators can be determined by independently optimizing the logical fidelity of the effective noise per syndrome.

关键词： quantum channels quantum communication quantum computation quantum error correction quantum fluctuations & noise quantum information processing quantum measurements quantum memories quantum theory Surface code quantum computing

Physical origins of ruled surfaces on the reduced density matrices geometry

学校读者我要写书评

暂无评论

science China(Physics,Mechanics & Astronomy) 2017年第2期60卷 1-8页

作者： Ji-Yao Chen Zhengfeng Ji Zheng-Xin Liu Xiaofei Qi Nengkun Yu Bei Zeng Duanlu Zhou State Key Laboratory of Low Dimensional Quantum Physics Department of Physics Tsinghua University Beijing 100084 China Perimeter Institute for Theoretical Physics Waterloo N2L 2Y5 Canada Centre for Quantum Computation ＆ Intelligent Systems School of Software Faculty of Engineering and Information Technology University of Technology Sydney Sydney 2007 Australia State Key Laboratory of Computer Science Institute of Software Chinese Academy of Sciences Beijing 100190 China Department of Physics Renmin University of China Beijing 100872 China Department of Mathematics Shanxi University Taiyuan 030000 China Institute for Quantum Computing University of Waterloo Waterloo N2L 3G1 Canada Department of Mathematics ＆ Statistics University of Guelph Guelph N1G 2W1 Canada Institute of Physics Chinese Academy of Sciences Beijing 100190 China

The reduced density matrices （RDMs） of many-body quantum states form a convex set. The boundary of low dimensional projections of this convex set may exhibit nontrivial geometry such as ruled surfaces. In this paper, we study the physical origins of these ruled surfaces for bosonic systems. The emergence of ruled surfaces was recently proposed as signatures of symmetry- breaking phase. We show that, apart from being signatures of symmetry-brealdng, ruled surfaces can also be the consequence of gapless quantum systems by demonstrating an explicit example in terms of a two-mode Ising model. Our analysis was largely simplified by the quantum de Finetti＇s theorem--in the limit of large system size, these RDMs are the convex set of all the symmetric separable states. To distinguish ruled surfaces originated from gapless systems from those caused by symmetry- breaking, we propose to use the finite size scaling method for the corresponding geometry. This method is then applied to the two-mode XY model, successfully identifying a ruled surface as the consequence of gapless systems.

关键词： ruled surfaces reduced density matrices bosonic system geometry

quantum speed-up in solving the maximal clique problem

学校读者我要写书评

暂无评论

arXiv 2018年

作者： Chang, Weng-Long Yu, Qi Li, Zhaokai Chen, Jiahui Peng, Xinhua Feng, Mang Department of Computer Science National Kaohsiung University of Applied Sciences Kaohsiung City80778 Taiwan CAS Key Laboratory of Microscale Magnetic Resonance Department of Modern Physics University of Science and Technology of China Hefei230026 China Synergetic Innovation Center of Quantum Information and Quantum Physics University of Science and Technology of China Hefei China Institute for Quantum Computing and Department of Physics and Astronomy University of Waterloo WaterlooON Canada State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics Wuhan Institute of Physics and Mathematics Chinese Academy of Sciences Wuhan430071 China Hunan Normal University Changsha410081 China Department of Physics Zhejiang Normal University Jinhua321004 China

The maximal clique problem, to find the maximally sized clique in a given graph, is classically an NP-complete computational problem, which has potential applications ranging from electrical engineering, computational chemistry, bioinformatics to social networks. Here we develop a quantum algorithm to solve the maximal clique problem for any graph G with n vertices with quadratic speed-up over its classical counterparts, where the time and spatial complexities are reduced to, respectively, O(√2n) and O(n2). With respect to oracle-related quantum algorithms for the NP-complete problems, we identify our algorithm to be optimal. To justify the feasibility of the proposed quantum algorithm, we have successfully solved an exemplified clique problem for a graph G with two vertices and one edge by carrying out a nuclear magnetic resonance experiment involving four qubits. Copyright © 2018, The Authors. All rights reserved.

关键词： quantum theory

Enhanced entanglement criterion via symmetric informationally complete measurements

学校读者我要写书评

暂无评论

Physical Review A 2018年第2期98卷 022309-022309页

作者： Jiangwei Shang Ali Asadian Huangjun Zhu Otfried Gühne Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems School of Physics Beijing Institute of Technology Beijing 100081 China Naturwissenschaftlich-Technische Fakultät Universität Siegen Walter-Flex-Straße 3 57068 Siegen Germany Department of Physics Institute for Advanced Studies in Basic Sciences (IASBS) Gava Zang Zanjan 45137-66731 Iran Vienna Center for Quantum Science and Technology Atominstitut TU Wien 1040 Vienna Austria Department of Physics and Center for Field Theory and Particle Physics Fudan University Shanghai 200433 China State Key Laboratory of Surface Physics Fudan University Shanghai 200433 China Institute for Nanoelectronic Devices and Quantum Computing Fudan University Shanghai 200433 China Collaborative Innovation Center of Advanced Microstructures Nanjing 210093 China Institute for Theoretical Physics University of Cologne Cologne 50937 Germany

We show that a special type of measurements, called symmetric informationally complete positive operator-valued measures (SIC POVMs), provide a stronger entanglement detection criterion than the computable cross-norm or realignment criterion based on local orthogonal observables. As an illustration, we demonstrate the enhanced entanglement detection power in simple systems of qubit and qutrit pairs. This observation highlights the significance of SIC POVMs for entanglement detection.

关键词： Entanglement detection quantum entanglement quantum measurements