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Quantum Causal Unravelling

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arXiv 2021年

作者： Bai, Ge Wu, Ya-Dong Zhu, Yan Hayashi, Masahito Chiribella, Giulio QICI Quantum Information and Computation Initiative Department of Computer Science The University of Hong Kong Pokfulam Road Hong Kong HKU-Oxford Joint Laboratory for Quantum Information and Computation United Kingdom Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China Guangdong Provincial Key Laboratory of Quantum Science and Engineering Southern University of Science and Technology Shenzhen518055 China Graduate School of Mathematics Nagoya University Nagoya464-8602 Japan Department of Computer Science University of Oxford Parks Road OxfordOX1 3QD United Kingdom Perimeter Institute For Theoretical Physics 31 Caroline Street North WaterlooONN2L 2Y5 Canada

Complex processes often arise from sequences of simpler interactions involving a few particles at a time. These interactions, however, may not be directly accessible to experiments. Here we develop the first efficient method for unravelling the causal structure of the interactions in a multipartite quantum process, under the assumption that the process has bounded information loss and induces causal dependencies whose strength is above a fixed (but otherwise arbitrary) threshold. Our method is based on a quantum algorithm whose complexity scales polynomially in the total number of input/output systems, in the dimension of the systems involved in each interaction, and in the inverse of the chosen threshold for the strength of the causal dependencies. Under additional assumptions, we also provide a second algorithm that has lower complexity and requires only local state preparation and local measurements. Our algorithms can be used to identify processes that can be characterized efficiently with the technique of quantum process tomography. Similarly, they can be used to identify useful communication channels in quantum networks, and to test the internal structure of uncharacterized quantum circuits. Copyright © 2021, The Authors. All rights reserved.

关键词： computational complexity

Unification of valley and anomalous Hall effects in a strained lattice

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arXiv 2021年

作者： Yuan, Jiale Cai, Han Wu, Congjun Zhu, Shi-Yao Liu, Ren-Bao Wang, Da-Wei Interdisciplinary Center for Quantum Information State Key Laboratory of Modern Optical Instrumentation Zhejiang Province Key Laboratory of Quantum Technology and Device Department of Physics Zhejiang University Hangzhou310027 China School of Science Westlake University Hangzhou310024 China Department of Physics Centre for Quantum Coherence Hong Kong Institute of Quantum Information Science and Technology Chinese University of Hong Kong Shatin N. T. Hong Kong CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing100190 China

Two dimensional lattices are an important stage for studying many aspects of quantum physics, in particular the topological phases. The valley Hall and anomalous Hall effects are two representative topological phenomena. Here we show that they can be unified in a strained honeycomb lattice, where the hopping strengths between neighboring sites are designed by mimicking those between the Fock states in a three-mode Jaynes-Cummings model. Such a strain induces an effective magnetic field which results in quantized Landau levels. The eigenstates in the zeroth Landau level can be represented by the eigenstates of a large pseudo-spin. We find that the valley Hall current and the chiral edge current in the Haldane model correspond to the spin precession around different axes. Our study sheds light on connection between seemingly unrelated topological phases in condensed matter physics. © 2021, CC BY.

关键词： Landforms

Extending the atomic decomposition and many-body representation, a chemistry-motivated monomer-centered approach for machine learning potentials

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arXiv 2024年

作者： Yu, Qi Ma, Ruitao Qu, Chen Conte, Riccardo Nandi, Apurba Pandey, Priyanka Houston, Paul L. Zhang, Dong H. Bowman, Joel M. Department of Chemistry Fudan University Shanghai200438 China Independent Researcher TorontoONM9B0E3 Canada Dipartimento di Chimica Università degli Studi di Milano via Golgi 19 Milano20133 Italy Department of Physics and Materials Science University of Luxembourg Luxembourg CityL-1511 Luxembourg Department of Chemistry Cherry L. Emerson Center for Scientific Computation Emory University AtlantaGA30322 United States Department of Chemistry and Chemical Biology Cornell University IthacaNY14853 United States State Key Laboratory of Molecular Reaction Dynamics Dalian Institute of Chemical Physics Chinese Academy of Sciences Dalian116023 China Department of Chemistry and Biochemistry Georgia Institute of Technology AtlantaGA30332 United States

Most widely used machine learned (ML) potentials for condensed phase applications rely on many-body permutationally invariant polynomial (PIP) or atom-centered neural networks (NN). However, these approaches often lack chemical interpretability in atomistic energy decomposition and the computational efficiency of traditional force fields has not been fully achieved. Here, we present a novel method that combines aspects of both approaches, and achieves state-of-the-art balance of accuracy and force field-level speed. This method utilizes a monomer-centered representation, where the potential energy is decomposed into the sum of chemically meaningful monomeric energies. Without sophisticated neural network design, the structural descriptors of monomers are described by 1-body and 2-body effective interactions, enforced by appropriate sets of PIPs as inputs to the feed forward *** demonstrate the performance of this method through systematic assessments of models for gas-phase water trimer, liquid water, and also liquid CO2. The high accuracy, fast speed, and flexibility of this method provide a new route for constructing accurate ML potentials and enabling large-scale quantum and classical simulations for complex molecular systems. © 2024, CC BY.

关键词： Monomers

Ideal Weyl semimetal with 3D spin-orbit coupled ultracold quantum gas

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science Bulletin 2020年第24期65卷 2080-2085,M0005页

作者： Yue-Hui Lu Bao-Zong Wang Xiong-Jun Liu International Center for Quantum Materials and School of Physics Peking UniversityBeijing 100871China Collaborative Innovation Center of Quantum Matter Beijing 100871China Shanghai Branch National Laboratory for Physical Sciences at Microscale and Department of Modem PhysicsUniversity of Science and Technology of ChinaShanghai 201315China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of SciencesBeijing 100190China

There is an immense effort in search for various types of Weyl semimetals, of which the most fundamental phase consists of the minimal number of i.e. two Weyl points, but is hard to engineer in solids. Here we demonstrate how such fundamental Weyl semimetal can be realized in a maneuverable optical Raman lattice, with which the three-dimensional(3D) spin-orbit(SO) coupling is synthesised for ultracold atoms. In addition, a new novel Weyl phase with coexisting Weyl nodal points and nodal ring is also predicted here, and is shown to be protected by nontrivial linking numbers. We further propose feasible techniques to precisely resolve 3D Weyl band topology through 2D equilibrium and dynamical measurements. This work leads to the first realization of the most fundamental Weyl semimetal band and the 3D SO coupling for ultracold quantum gases, which are respectively the significant issues in the condensed matter and ultracold atom physics.

关键词： Weyl semimetal Spin-orbit coupling Topological quantum phase Ultracold atoms Optical lattice Quench dynamics

Anisotropic g-Factor and spin-orbit field in a ge hut wire double quantum dot

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arXiv 2021年

作者： Zhang, Ting Liu, He Gao, Fei Xu, Gang Wang, Ke Zhang, Xin Cao, Gang Wang, Ting Zhang, Jianjun Hu, Xuedong Li, Hai-Ou Guo, Guo-Ping CAS Key Laboratory of Quantum Information University of Science and Technology of China Anhui Hefei230026 China CAS Center for Excellence Synergetic Innovation Center in Quantum Information and Quantum Physics University of Science and Technology of China Anhui Hefei230026 China Institute of Physics CAS Center for Excellence in Topological Quantum Computation Chinese Academy of Sciences Beijing100190 China Department of Physics University at Buffalo SUNY BuffaloNY14260 United States Origin Quantum Computing Company Limited Anhui Hefei230026 China

Holes in nanowires have drawn significant attention in recent years because of the strong spin-orbit interaction, which plays an important role in constructing Majorana zero modes and manipulating spin-orbit qubits. Here, from the strongly anisotropic leakage current in the spin blockade regime for a double dot, we extract the full g-tensor and find that the spin-orbit field is in plane with an azimuthal angle of 59° to the axis of the nanowire. The direction of the spin-orbit field indicates a strong spin-orbit interaction along the nanowire, which may have originated from the interface inversion asymmetry in Ge hut wires. We also demonstrate two different spin relaxation mechanisms for the holes in the Ge hut wire double dot: spin-flip cotunneling to the leads, and spin-orbit interaction within the double dot. These results help establish feasibility of a Ge-based quantum processor. Copyright © 2021, The Authors. All rights reserved.

关键词： Semiconductor quantum dots

Variational Ansatz for the Ground State of the Quantum Sherrington-Kirkpatrick Model

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Physical Review Letters 2022年第22期129卷 220401-220401页

作者： Paul M. Schindler Tommaso Guaita Tao Shi Eugene Demler J. Ignacio Cirac Max-Planck-Institut für Physik komplexer Systeme Nöthnitzer Straße 38 01187 Dresden Germany Max-Planck-Institut für Quantenoptik Hans-Kopfermann-Straße 1 85748 Garching Germany Munich Center for Quantum Science and Technology Schellingstraße 4 80799 München Germany Dahlem Center for Complex Quantum Systems Freie Universität Berlin Arnimallee 14 14195 Berlin Germany CAS Key Laboratory of Theoretical Physics Institute of Theoretical Physics Chinese Academy of Sciences Beijing 100190 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing 100049 China Institute for Theoretical Physics ETH Zurich Wolfgang-Pauli-Straße 27 8093 Zurich Switzerland

We present an Ansatz for the ground states of the quantum Sherrington-Kirkpatrick model, a paradigmatic model for quantum spin glasses. Our Ansatz, based on the concept of generalized coherent states, very well captures the fundamental aspects of the model, including the ground state energy and the position of the spin glass phase transition. It further enables us to study some previously unexplored features, such as the nonvanishing longitudinal field regime and the entanglement structure of the ground states. We find that the ground state entanglement can be captured by a simple ensemble of weighted graph states with normally distributed phase gates, leading to a volume law entanglement, contrasting with predictions based on entanglement monogamy.

关键词： Glass transition Optimization problems Quantum entanglement Quantum spin models Spin glasses Approximation methods for many-body systems Trial wave functions

The Smoothed Wigner distribution, using past and future information, is not the Wigner function of the Smoothed Weak-Valued state

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arXiv 2025年

作者： Laverick, Kiarn T. Chantasri, Areeya Wiseman, Howard M. MajuLab CNRS-UCA-SU-NUS-NTU International Joint Research Laboratory France Centre for Quantum Technologies National University of Singapore Singapore117543 Singapore Optical and Quantum Physics Laboratory Department of Physics Faculty of Science Mahidol University Bangkok10140 Thailand Centre for Quantum Computation and Communication Technology Australian Research Council Quantum and Advanced Technologies Research Institute Griffith University Yuggera Country BrisbaneQLD4111 Australia

In this paper, we correct a mistake we made in [Phys. Rev. Lett. 122, 190402 (2019)] and [Phys. Rev. A 103, 012213 (2021)] regarding the Wigner function of the so-called smoothed Weak-Valued state (SWV state). Here smoothing refers to estimation of properties at time t using information obtained in measurements both before and after t. The SWV state is a pseudo-state (Hermitian but not necessarily positive) that gives, by the usual trace formula, the correct value for a weak measurement preformed at time t, i.e., its weak value. The Wigner function is a pseudo-probability-distribution (real but not necessarily positive) over phase-space. A smoothed (in this estimation sense) Wigner distribution at time t can also be defined by applying classical smoothing for probability-distributions to the Wigner functions. The smoothed Wigner distribution (SWD) gives identical means for the canonical phase-space variables as does the SWV state. However, contrary to the assumption in the above references, the Wigner function of the SWV state is not the smoothed Wigner distribution. © 2025, CC BY.

关键词： Wigner-Ville distribution

Giant Chern number of a Weyl nodal surface without upper limit

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arXiv 2022年

作者： Ma, Junzhang Zhang, S.-N. Song, J.P. Wu, Q.-S. Ekahana, S.A. Naamneh, M. Radovic, M. Strocov, V.N. Gao, S.-Y. Qian, T. Ding, H. He, K. Manna, K. Felser, C. Plumb, N.C. Yazyev, O.V. Xiong, Y.-M. Shi, M. Department of Physics City University of Hong Kong Kowloon Hong Kong Swiss Light Source Paul Scherrer Institute Villigen PSI CH-5232 Switzerland City University of Hong Kong Shenzhen Research Institute Shenzhen China Hong Kong Institute for Advanced Study City University of Hong Kong Kowloon Hong Kong Institute of Physics École Polytechnique Fédérale de Lausanne LausanneCH-10 15 Switzerland LausanneCH-1015 Switzerland Anhui Key Laboratory of Condensed Matter Physics at Extreme Conditions High Magnetic Field Laboratory HFIPS Anhui Chinese Academy of Sciences Hefei230031 China University of Science and Technology of China Anhui Hefei230026 China Department of Physics Ben-Gurion University of the Negev Beer-Sheva84105 Israel Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing100190 China Songshan Lake Materials Laboratory Guangdong Dongguan China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing100049 China Department of Physics Tsinghua University Beijing100084 China Max Planck Institute for Chemical Physics of Solids DresdenD-01187 Germany Department of Physics Indian Institute of Technology Delhi Hauz Khas New Delhi110016 India Department of Physics School of Physics and Optoelectronics Engineering Anhui University Hefei230601 China

Weyl nodes can be classified into zero-dimensional (0D) Weyl points (WPs), 1D Weyl nodal lines (WNL) and 2D Weyl nodal surfaces (WNS), which possess finite Chern numbers. Up to date, the largest Chern number of WPs identified in Weyl semimetals is 4, which is thought to be a maximal value for linearly crossing points in solids. On the other hand, whether the Chern numbers of nonzero-dimensional linear crossing Weyl nodal objects have one upper limit is still an open question. In this work, combining angle-resolved photoemission spectroscopy with density functional theory calculations, we show that the chiral crystal AlPt hosts a cubeshaped charged Weyl nodal surface which is formed by the linear crossings of two singly-degenerate bands. Different to conventional Weyl nodes, the cube-shaped nodal surface in AlPt is enforced by nonsymmorphic chiral symmetries and time reversal symmetry rather than accidental band crossings, and it possesses a giant Chern number |C| = 26. Moreover, our results and analysis prove that there is no upper limit for the Chern numbers of such kind 2D Weyl nodal object. © 2022, CC BY.

关键词： Density functional theory

MeerKAT discovery of GHz radio emission extending from Abell 3017 toward Abell 3016

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arXiv 2024年

作者： Hu, Dan Werner, Norbert Xu, Haiguang Zheng, Qian Breuer, Jean-Paul Wu, Linhui Duchesne, Stefan W. van Weeren, Reinout J. Sun, Ming Zhang, Congyao Johnston-Hollitt, Melanie Shan, Huanyuan Guo, Quan Zhu, Zhenghao Wang, Jingying Gu, Junhua Zhao, Yuanyuan Siew, Hoongwah Mao, Junjie Zhang, Zhongli Plšek, Tomáš Department of Theoretical Physics and Astrophysics Faculty of Science Masaryk University Kotlářská 2 Brno611 37 Czech Republic School of Physics and Astronomy Shanghai Jiao Tong University Dongchuan Road 800 Shanghai200240 China Shanghai Astronomical Observatory Chinese Academy of Sciences Nandan Road 80 Shanghai China Department of Physics Graduate School of Advanced Science and Engineering Hiroshima University Kagamiyama 1-3-1 Higashi-Hiroshima739-8526 Japan CSIRO Space & Astronomy PO Box 1130 BentleyWA6102 Australia Leiden Observatory Leiden University PO Box 9513 Leiden2300 RA Netherlands Department of Physics and Astronomy University of Alabama in Huntsville HuntsvilleAL35899 United States Curtin Institute for Computation Curtin University GPO Box U1987 PerthWA6845 Australia National Astronomical Observatories Chinese Academy of Sciences 20A Datun Road Beijing100101 China Department of Astronomy Tsinghua University Beijing100084 China Key Laboratory of Radio Astronomy and Technology Chinese Academy of Sciences A20 Datun Road Chaoyang District Beijing100101 China

Context. Cosmic filaments are vast, faint structures that connect galaxy clusters, often challenging to detect directly. However, filaments between pre-merger cluster pairs become more visible due to gas heating and compression while the clusters are approaching, enabling detection in X-ray and radio wavelengths. The clusters Abell 3017 and Abell 3016 are located within such a large-scale filament. A prominent X-ray bridge has been detected connecting the two clusters and a potential galaxy group between them. Aims. The aim of this work is to investigate the existence of a radio bridge in the filament between Abell 3017 and Abell 3016, to explore other diffuse radio structures within this system, and to investigate the origins of these diffuse radio emission. Methods. We analyzed MeerKAT L-band data to study the morphology and spectra of the diffuse radio structures in Abell 3016-Abell 3017. X-ray imaging and spectral analysis were carried out with archival Chandra and XMM-Newton data. Additionally, correlations between radio (IR) and X-ray surface brightness (IX) were generated to explore the connections between thermal and non-thermal components in the diffuse radio emission. Results. We detected a faint radio bridge with an average surface brightness of ∼ 0.1 µJy arcsec−2 at 1280 MHz using MeerKAT. It connects Abell 3017 with a potential galaxy group and extends towards Abell 3016, aligning with the X-ray bridge. A high X-ray temperature of 7.09±0.54 keV detected in the bridge region suggests an interaction between Abell 3017 and the group. In Abell 3017, we identified two distinct components of diffuse radio emission: a radio mini-halo and an outer radio halo with a northern extension (N-extension hereafter). The radio surface brightness profile of Abell 3017 shows a steep inner component consistent with other mini-halos, and a faint outer component likely linked to an infalling subcluster. The IR − IX diagram indicates superlinear and sublinear correlations for

关键词： Cosmology