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Neutron spin echo is a "quantum tale of two paths"

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arXiv 2023年

作者： McKay, S. Irfan, A.A.M. Thien, Q. Le Geerits, N. Parnell, S.R. Dalgliesh, R.M. Lavrik, N.V. Kravchenko, I.I. Ortiz, G. Pynn, R. Department of Physics Indiana University BloomingtonIN47405 United States Center for Exploration of Energy and Matter Indiana University Bloomington47408 United States Institute for Quantum Computing University of Waterloo WaterlooONN2L 3G1 Canada Atominstitut TU Wien Stadionallee 2 Vienna1020 Austria Faculty of Applied Sciences Delft University of Technology Mekelweg 15 Delft2629 JB Netherlands ISIS Rutherford Appleton Laboratory Oxfordshire ChiltonOX11 0QX United Kingdom Center for Nanophase Materials Science Oak Ridge National Laboratory Oak RidgeTN37831 United States Quantum Science and Engineering Center Indiana University BloomingtonIN47408 United States Neutron Sciences Directorate Oak Ridge National Laboratory Oak RidgeTN37830 United States

We describe an experiment that strongly supports a two-path interferometric model in which the spin-up and spin-down components of each neutron propagate coherently along spatially separated parallel paths in a typical neutron spin echo small angle scattering (SESANS) experiment. Specifically, we show that the usual semi-classical, single-path treatment of Larmor precession of a polarized neutron in an external magnetic field predicts a damping as a function of the spin echo length of the SESANS signal obtained with a periodic phase grating when the transverse width of the neutron wave packet is finite. However, no such damping is observed experimentally, implying either that the Larmor model is incorrect or that the transverse extent of the wave packet is very large. In contrast, we demonstrate theoretically that a quantum-mechanical interferometric model in which the two mode-entangled (i.e. intraparticle entangled) spin states of a single neutron are separated in space when they interact with the grating accurately predicts the measured SESANS signal, which is independent of the wave packet width. Copyright © 2023, The Authors. All rights reserved.

关键词： Damping

Algebraic higher symmetry and categorical symmetry: A holographic and entanglement view of symmetry

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Physical Review Research 2020年第4期2卷 043086-043086页

作者： Liang Kong Tian Lan Xiao-Gang Wen Zhi-Hao Zhang Hao Zheng Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 People's Republic of China Guangdong Provincial Key Laboratory of Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 People's Republic of China Institute for Quantum Computing University of Waterloo Waterloo Ontario N2L 3G1 Canada Department of Physics Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA School of Mathematical Sciences University of Science and Technology of China Hefei 230026 People's Republic of China Department of Mathematics Peking University Beijing 100871 People's Republic of China

A global symmetry (0-symmetry) in an n-dimensional space acts on the whole space. A higher symmetry acts on closed submanifolds (i.e., loops and membranes, etc.), and those transformations form a higher group. In this paper, we introduce the notion of algebraic higher symmetry, which generalizes higher symmetry and is beyond higher group. We show that an algebraic higher symmetry in a bosonic system in n-dimensional space is characterized and classified by a local fusion n-category. We find that, when restricted to its symmetric sub-Hilbert space, an algebraic higher symmetry can be fully characterized by a noninvertible gravitational anomaly (i.e., a topological order in one higher dimension). Thus, we also refer to a noninvertible gravitational anomaly as categorical symmetry to stress its connection to symmetry. This provides a holographic and entanglement view of symmetries. For a system with a categorical symmetry, its gapped state must spontaneously break part (not all) of the symmetry, and the state with the full symmetry must be gapless. Using such a holographic point of view, we obtain (1) the gauging of the algebraic higher symmetry; (2) the classification of anomalies for an algebraic higher symmetry; (3) the equivalence between classes of systems, with different (potentially anomalous) algebraic higher symmetries or different sets of low-energy excitations, as long as they have the same categorical symmetry; and (4) the classification of gapped liquid phases for bosonic and/or fermionic systems with a categorical symmetry, as gapped boundaries of a topological order in one higher dimension (that corresponds to the categorical symmetry). This classification includes symmetry protected trivial (SPT) orders and symmetry enriched topological (SET) orders with an algebraic higher symmetry.

关键词： Topological field theories Topological phases of matter Topological quantum computing

Naive lattice fermion without doublers

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Physical Review D 2021年第9期104卷 094505-094505页

作者： Xingyu Guo Chen-Te Ma Hui Zhang Guangdong Provincial Key Laboratory of Nuclear Science Institute of Quantum Matter South China Normal University Guangzhou Guangdong 510006 China Guangdong-Hong Kong Joint Laboratory of Quantum Matter Southern Nuclear Science Computing Center South China Normal University Guangzhou Guangdong 510006 China Asia Pacific Center for Theoretical Physics Pohang University of Science and Technology Pohang Gyeongsangbuk-do 37673 South Korea School of Physics and Telecommunication Engineering South China Normal University Guangzhou Guangdong 510006 China Laboratory for Quantum Gravity and Strings Department of Mathematics and Applied Mathematics University of Cape Town Private Bag Rondebosch 7700 South Africa

We discuss the naive lattice fermion without the issue of doublers. A local lattice massless fermion action with chiral symmetry and Hermiticity cannot avoid the doubling problem from the Nielsen-Ninomiya theorem. Here we adopt the forward finite-difference deforming the γ5-Hermiticity but preserving the continuum chiral symmetry. The lattice momentum is not Hermitian without the continuum limit now. We demonstrate that there is no doubling issue from an exact solution. The propagator only has one pole in the first-order accuracy. Therefore, it is hard to know the avoiding due to the non-Hermiticity. For the second-order, the lattice propagator has two poles as before. This case also does not suffer from the doubling problem. Hence separating the forward derivative from the backward one evades the doublers under the field theory limit. Simultaneously, it is equivalent to breaking the Hermiticity. In the end, we discuss the topological charge and also demonstrate the numerical implementation of the hybrid Monte Carlo.

关键词： Lattice field theory quantum field theory Chiral symmetry Hybrid Monte Carlo algorithm

engineering the level structure of a giant artificial atom in waveguide quantum electrodynamics

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arXiv 2020年

作者： Vadiraj, A.M. Ask, Andreas McConkey, T.G. Nsanzineza, I. Chang, C.W. Sandbo Kockum, Anton Frisk Wilson, C.M. Institute for Quantum Computing and Electrical and Computer Engineering University of Waterloo WaterlooONN2L 3G1 Canada Department of Microtechnology and Nanoscience Chalmers University of Technology Gothenburg412 96 Sweden

engineering light-matter interactions at the quantum level has been central to the pursuit of quantum optics for decades. Traditionally, this has been done by coupling emitters, typically natural atoms and ions, to quantized electromagnetic fields in optical and microwave cavities. In these systems, the emitter is approximated as an idealized dipole, as its physical size is orders of magnitude smaller than the wavelength of light. Recently, artificial atoms made from superconducting circuits have enabled new frontiers in light-matter coupling, including the study of "giant" atoms which cannot be approximated as simple dipoles. Here, we explore a new implementation of a giant artificial atom, formed from a transmon qubit coupled to propagating microwaves at multiple points along an open transmission line. The nature of this coupling allows the qubit radiation field to interfere with itself leading to some striking giant-atom effects. For instance, we observe strong frequency-dependent couplings of the qubit energy levels to the electromagnetic modes of the transmission line. Combined with the ability to in situ tune the qubit energy levels, we show that we can modify the relative coupling rates of multiple qubit transitions by more than an order of magnitude. By doing so, we engineer a metastable excited state, allowing us to operate the giant transmon as an effective lambda system where we clearly demonstrate electromagnetically induced transparency. Copyright © 2020, The Authors. All rights reserved.

关键词： Atoms

Nonreciprocal transport in a bilayer of MnBi2Te4 and Pt

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arXiv 2022年

作者： Ye, Chen Xie, Xiangnan Lv, Wenxing Huang, Ke Yang, Allen Jian Jiang, Sicong Liu, Xue Zhu, Dapeng Qiu, Xuepeng Tong, Mingyu Zhou, Tong Hsu, Chuang-Han Chang, Guoqing Lin, Hsin Li, Peisen Yang, Kesong Wang, Zhenyu Jiang, Tian Wang, Xiao Renshaw Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University 21 Nanyang Link 637371 Singapore State Key Laboratory of High Performance Computing College of Computer Science and Technology National University of Defense Technology Changsha410073 China Physics Laboratory Industrial Training Center Shenzhen Polytechnic Guangdong Shenzhen518055 China Department of NanoEngineering Program of Chemical Engineering University of California La Jolla San DiegoCA92093-0448 United States Program of Materials Science and Engineering University of California La Jolla San DiegoCA92093-0418 United States Institutes of Physical Science and Information Technology Anhui University Hefei230601 China Fert Beijing Institute MIIT Key Laboratory of Spintronics School of Integrated Circuit Science and Engineering Beihang University Beijing100191 China Beihang-Goertek Joint Microelectronics Institute Qingdao Research Institute Beihang University Qingdao266000 China Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology School of Physics Science and Engineering Tongji University Shanghai200092 China College of Advanced Interdisciplinary Studies National University of Defense Technology Changsha410073 China Insitute of Physics Academia Sinica Taipei115229 Taiwan College of Intelligence Science and Technology National University of Defense Technology Changsha410073 China National Innovation Institute of Defense Technology Academy of Military Sciences PLA China Beijing100010 China Beijing Academy of Quantum Information Sciences Beijing100084 China Beijing Institute for Advanced Study National University of Defense Technology Changsha410073 China School of Electrical and Electronic Engineering Nanyang Technological University 50 Nanyang Ave 639798 Singapore

MnBi2Te4 (MBT) is the first intrinsic magnetic topological insulator with the interaction of spin-momentum locked surface electrons and intrinsic magnetism, and it exhibits novel magnetic and topological phenomena. Recent studies suggested that the interaction of electrons and magnetism can be affected by the Mn-doped Bi2Te3 phase at the surface due to inevitable structural defects. Here we report an observation of nonreciprocal transport, i.e. current-direction-dependent resistance, in a bilayer composed of antiferromagnetic MBT and nonmagnetic Pt. The emergence of the nonreciprocal response below the Néel temperature confirms a correlation between nonreciprocity and intrinsic magnetism in the surface state of MBT. The angular dependence of the nonreciprocal transport indicates that nonreciprocal response originates from the asymmetry scattering of electrons at the surface of MBT mediated by magnon. Our work provides an insight into nonreciprocity arising from the correlation between magnetism and Dirac surface electrons in intrinsic magnetic topological insulators. © 2022, CC BY.

关键词： Magnetism

Impact of the central frequency of environment on non-markovian dynamics in piezoelectric optomechanical devices

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arXiv 2020年

作者： Ding, Quanzhen Zhao, Peng Ma, Yonghong Chen, Yusui Department of Physics Center for Quantum Science and Engineering Stevens Institute of Technology HobokenNJ07030 United States Department of Physics New York Institute of Technology Old WestburyNY11568 United States Department of Engineering and Computing Sciences New York Institute of Technology Old WestburyNY11568 United States School of Science Inner Mongolia University of Science and Technology Baotou014010 China

The piezoelectric optomechanical devices supply a promising experimental platform to realize the coherent and effective control and measurement on optical circuits working in Terahertz (THz) frequencies via superconducting electron devices typically working in Radio (MHz) frequencies. However, quantum fluctuations are unavoidable when the size of mechanical oscillators enter into the nanoscale. The consequences of the noisy environment is still challenging due to the lack of analytical tools. In this paper, a semi-classical and full-quantum model of piezoelectric optomechanical systems coupled to a noisy bosonic quantum environment are introduced and solved in terms of quantum-state diffusion (QSD) trajectories in the non-Markovian regime. We show that the noisy environment, particularly the central frequency of environment, can enhance the entanglement generation between optical cavities and LC circuits in some parameter regimes. Moreover, we observe the critical points in the coefficient functions, which can lead the different behaviors in the system. Besides, we also witness the entanglement transfers between macroscopic objects due to the memory effect of the environment. Our work can be applied in the fields of electric/ optical switches, and long-distance distribution in large-scale quantum network. © 2020, CC-BY.

关键词： Piezoelectricity

Electric-magnetic duality in twisted quantum double model of topological orders

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arXiv 2020年

作者： Hu, Yuting Wan, Yidun Department of Physics Institute for Quantum Science and Engineering South University of Science and Technology Shenzhen518055 China State Key Laboratory of Surface Physics Fudan University Shanghai200433 China Department of Physics Center for Field Theory and Particle Physics Institute for Nanoelectronic devices and Quantum computing Fudan University Shanghai200433 China

We derive a partial electric-magnetic (PEM) duality transformation of the twisted quantum double (TQD) model TQD(G,α)—discrete Dijkgraaf-Witten model—with a finite gauge group G, which has an Abelian normal subgroup N, and a three-cocycle α ∈ H3(G,U(1)). Any equivalence between two TQD models, say, TQD(G,α) and TQD(G0,α0), can be realized as a PEM duality transformation, which exchanges the N-charges and N-fluxes only. Via the PEM duality, we construct an explicit isomorphism between the corresponding TQD algebras Dα(G) and Dα0(G0) and derive the map between the anyons of one model and those of the other. Copyright © 2020, The Authors. All rights reserved.

关键词： quantum theory

Permutation enhances classical communication assisted by entangled states

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arXiv 2020年

作者： Wang, Kun Hayashi, Masahito Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China Center for Quantum Computing Peng Cheng Laboratory Shenzhen518055 China Graduate School of Mathematics Nagoya University Nagoya464-8602 Japan Centre for Quantum Technologies National University of Singapore 3 Science Drive 2 Singapore117542 Singapore

We give a capacity formula for the classical communication over a noisy quantum channel, when local operations and global permutations allowed in the encoding and bipartite states preshared between the sender and the receiver. The two endpoints of this formula are the Holevo capacity (without entanglement assistance) and the entanglementassisted capacity (with unlimited entanglement assistance). What's more, we show that the capacity satisfies the strong converse property and thus the formula serves as a sharp dividing line between achievable and unachievable rates of communication. We prove that the difference between the assisted capacity and the Holevo capacity is upper bounded by the discord of formation of the preshared state. As examples, we derive analytically the classical capacity of various quantum channels of interests. Our result witnesses the power of random permutation in classical communication, whenever entanglement assistance is available. Copyright © 2020, The Authors. All rights reserved.

关键词： quantum entanglement

Subspace controllability of symmetric spin networks

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Physical Review A 2020年第3期102卷 032602-032602页

作者： Jiahui Chen Yehao Zhou Ji Bian Jun Li Xinhua Peng Department of Physics University of Waterloo Waterloo Ontario Canada N2L 3G1 Institute for Quantum Computing Waterloo Ontario Canada N2L 3G1 Perimeter Institute for Theoretical Physics Waterloo Ontario Canada N2L 2Y5 Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics University of Science and Technology of China Hefei Anhui 230026 China Chinese Academy of Sciences Key Laboratory of Microscale Magnetic Resonance University of Science and Technology of China Hefei Anhui 230026 China Shenzhen Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and Technology Shenzhen 518055 China Center for Quantum Computing Peng Cheng Laboratory Shenzhen 518055 China

Controlling the dynamics of quantum systems has been a long-standing goal of quantum physics. To understand the controllability of a finite-dimensional quantum system is a fundamental problem in quantum control theory, but can be very challenging in many cases. In particular, results on controllability of open-loop coherently controlled closed quantum systems under symmetry constraints have been elusive. In this paper, we study the controllability of spin systems with some specific symmetry where spins are coupled via Ising interaction and manipulated collectively by a global control field. Based on Lie group and Lie algebra techniques, we find the conditions under which the system is universally controllable in its irreducible subspaces. We believe that the results obtained here will contribute to quantum controlling on symmetric quantum systems.

关键词： quantum control