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General framework for verifying pure quantum states in the adversarial scenario

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Physical Review A 2019年第6期100卷 062335-062335页

Bipartite and multipartite entangled states are of central interest in quantum information processing and foundational studies. Efficient verification of these states, especially in the adversarial scenario, is a key to various applications, including quantum computation, quantum simulation, and quantum networks. However, little is known about this topic in the adversarial scenario. Here we initiate a systematic study of pure-state verification in the adversarial scenario. In particular, we introduce a general method for determining the minimal number of tests required by a given strategy to achieve a given precision. In the case of homogeneous strategies, we can even derive an analytical formula. Furthermore, we propose a general recipe to verifying pure quantum states in the adversarial scenario by virtue of protocols for the nonadversarial scenario. Thanks to this recipe, the resource cost for verifying an arbitrary pure state in the adversarial scenario is comparable to the counterpart for the nonadversarial scenario, and the overhead is at most three times for high-precision verification. Our recipe can readily be applied to efficiently verify bipartite pure states, stabilizer states, hypergraph states, weighted graph states, and Dicke states in the adversarial scenario, even if only local projective measurements are accessible. This paper is an extended version of the companion paper Zhu and Hayashi, Phys. Rev. Lett. 123, 260504 (2019).

关键词： Quantum entanglement Quantum tomography

Optimal verification and fidelity estimation of maximally entangled states

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Physical Review A 2019年第5期99卷 052346-052346页

作者： Huangjun Zhu Masahito Hayashi 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 Graduate School of Mathematics Nagoya University Nagoya 464-8602 Japan Shenzhen Institute for Quantum Science and Engineering Southern University of Science and Technology Shenzhen 518055 China Centre for Quantum Technologies National University of Singapore 3 Science Drive 2 117542 Singapore

We study the verification of maximally entangled states by virtue of the simplest measurement settings: local projective measurements without adaption. We show that optimal protocols are in one-to-one correspondence with complex projective 2-designs constructed from orthonormal bases. Optimal protocols with minimal measurement settings are in one-to-one correspondence with complete sets of mutually unbiased bases. Based on this observation, optimal protocols are constructed explicitly for any local dimension, which can also be applied to estimating the fidelity with the target state and to detecting entanglement. In addition, we show that incomplete sets of mutually unbiased bases are optimal for verifying maximally entangled states when the number of measurement settings is restricted. Moreover, we construct optimal protocols for the adversarial scenario in which state preparation is not trusted. The number of tests has the same scaling behavior as the counterpart for the nonadversarial scenario; the overhead is no more than three times. We also show that the entanglement of the maximally entangled state can be certified with any given significance level using only one test as long as the local dimension is large enough.

关键词： Quantum entanglement Quantum tomography

Direct observation of heavy quasiparticles in the Kondo lattice CeIn3

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arXiv 2018年

作者： Zhang, Y. Feng, W. Lou, X. Yu, T.L. Zhu, X.G. Tan, S.Y. Yuan, B.K. Liu, Y. Lu, H.Y. Xie, D.H. Liu, Q. Zhang, W. Luo, X.B. Huang, Y.B. Luo, L.Z. Zhang, Z.J. Lai, X.C. Chen, Q.Y. Science and Technology on Surface Physics and Chemistry Laboratory Mianyang621907 China Department of Engineering Physics Tsinghua University Beijing100084 China State Key Laboratory of Surface Physics Department of Physics Fudan University Shanghai200433 China Shanghai Institute of Applied Physics Chinese Academy of Sciences Shanghai201204 China Key Laboratory of Advanced Materials School of Materials Science and Engineering Tsinghua University Beijing100084 China

The electronic structure of the Kondo lattice CeIn3 has been studied by on-resonant angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. A weakly dispersive quasiparticle band has been observed directly with an energy dispersion of 4 meV by photoemission, implying the existence of weak hybridization between the f electrons and conduction electrons. The hybridization is further confirmed by the formation of the hybridization gap revealed by temperature-dependent scanning tunneling spectroscopy. Moreover, we find the hybridization strength in CeIn3 is much weaker than that in the more two-dimensional compounds CeCoIn5 and CeIrIn5. Our results may be essential for the complete microscopic understanding of this important compound and the related heavy-fermion systems. Copyright © 2018, The Authors. All rights reserved.

关键词： Indium alloys

Electronic structure and 4 f-electron character in Ce2PdIn8studied by angle-resolved photoemission spectroscopy

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arXiv 2019年

作者： Yao, Q. Kaczorowski, D. Swatek, P. Gnida, D. Wen, C.H.P. Niu, X.H. Peng, R. Xu, H.C. Dudin, P. Kirchner, S. Chen, Q.Y. Shen, D.W. Feng, D.L. State Key Laboratory of Surface Physics Department of Physics Laboratory of Advanced Materials Fudan University Shanghai200438 China Chinese Academy of Sciences Shanghai200050 China Institute of Low Temperature and Structure Research Polish Academy of Sciences P. O. Box 1410 Wroclaw50-950 Poland Centre for Advanced Materials and Smart Structures Polish Academy of Sciences Okolna 2 Wroclaw50-422 Poland Division of Materials Science and Engineering Ames Laboratory AmesIA50011 United States Department of Physics and Astronomy Iowa State University AmesIA50011 United States Diamond Light Source Harwell Science and Innovation Campus DidcotOX11 0DE United Kingdom Zhejiang Institute of Modern Physics Zhejiang University Hangzhou Zhejiang310027 China Science and Technology on Surface Physics and Chemistry Laboratory Mianyang621908 China Shanghai200050 China Collaborative Innovation Center of Advanced Microstructures Nanjing210093 China

The localized-to-itinerant transition of f electrons lies at the heart of heavy fermion physics, but has only been directly observed in single-layer Ce-based materials. Here we report a comprehensive study on the electronic structure and nature of the Ce 4 f electrons in the heavy fermion superconductor Ce2PdIn8, a typical n=2 CenMmIn3n+2mcompound, using high-resolution and 4d-4 f resonant photoemission spectroscopies. The electronic structure of this material has been studied over a wide temperature range, and hybridization between f and conduction electrons can be clearly observed to form Kondo resonance near the Fermi level at low temperature. The characteristic temperature of the localized-to-itinerant transition is around 120 K, which is much higher than its coherence temperature Tcoh∼ 30 K. Copyright © 2019, The Authors. All rights reserved.

关键词： Electronic structure

Gapped Spin-1/2 Spinon Excitations in a New Kagome Quantum Spin Liquid Compound Cu_3Zn(OH)_6FBr

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Chinese Physics Letters 2017年第7期34卷 249-253页

作者：冯子力李政孟鑫衣玮魏源张骏王艳成蒋伟刘峥李世燕刘锋雒建林李世亮郑国庆孟子杨梅佳伟石友国 Institute of Physics Chinese Academy of Sciences School of Physical Sciences University of Chinese Academy of Sciences State Key Laboratory of Surface Physics Department of Physics and Laboratory of Advanced Materials Fudan University Department of Materials Science and Engineering University of Utah Institute for Advanced Study Tsinghua University Collaborative Innovation Center of Advanced Microstructures Collaborative Innovation Center of Quantum Matter Department of Physics Okayama University Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and Technology Beijing Computational Science Research Center

We report a new kagome quantum spin liquid candidate CuaZn（OH）6FBr, which does not experience any phase transition down to 50inK, more than three orders lower than the antiferromagnetic Curie-Weiss temperature （-200 K）. A clear gap opening at low temperature is observed in the uniform spin susceptibility obtained from 19F nuclear magnetic resonance measurements. We observe the characteristic magnetic field dependence of the gap as expected for fractionalized spin-1/2 spinon excitations. Our experimental results provide firm evidence for spin fractionalization in a topologically ordered spin system, resembling charge fraetionalization in the fractional quantum Hall state.

关键词： OH Gapped Spin-1/2 Spinon Excitations in a New Kagome Quantum Spin Liquid Compound Cu3Zn Cu

Ferroelectricity with asymmetric hysteresis in metallic LiOsO3 ultrathin films

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arXiv 2019年

作者： Lu, Jinlian Chen, Gong Luo, Wei Íñiguez, Jorge Bellaiche, Laurent Xiang, Hongjun State Key Laboratory of Surface Physics Department of Physics Fudan University Shanghai200433 China Collaborative Innovation Center of Advanced Microstructures Nanjing210093 China Department of Physics University of Science and Technology of China Hefei230026 China Materials Research and Technology Department Luxembourg Institute of Science and Technology 5 Avenue des Hauts-Fourneaux Esch/AlzetteL-4362 Luxembourg Physics and Materials Science Research Unit University of Luxembourg 41 Rue du Brill BelvauxL-4422 Luxembourg Physics Department Institute for Nanoscience and Engineering University of Arkansas FayettevilleAR72701 United States

Bulk LiOsO3 was experimentally identified as a "ferroelectric" metal where polar distortions coexist with metallicity [Shi et al., Nature Materials 12, 1024 (2013)]. It is generally believed that polar displacements in a "ferroelectric" metal cannot be switched by an external electric field. Here, via comprehensive density functional theory calculations, we demonstrate that a two-unit-cell-thick LiOsO3 thin film exhibits a ferroelectric ground state having an out-of-plane electric dipole moment that can be switched by an external electric field. Moreover, its dipole moment-versus-electric-field hysteresis loop is asymmetric because only surface Li ions’ displacements are reversed by external electric field whereas the field-induced force on inner Li atoms are nearly fully screened by itinerant electrons. As a relevant by-product of our study, we also extend the concept of "Born effective charge" to finite metallic systems, and show its usefulness to rationalize the observed effects. Copyright © 2019, The Authors. All rights reserved.

关键词： Ferroelectricity

Correction: Zero-thermal-quenching and photoluminescence tuning with the assistance of carriers from defect cluster traps

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Journal of Materials Chemistry C 2019年第35期7卷 11040-11040页

作者： Yali Chen Binxun Yu Jing Gou Shengzhong Frank Liu Key Laboratory of Applied Surface and Colloid Chemistry Ministry of Education Shaanxi Key Laboratory for Advanced Energy Devices Shaanxi Engineering Lab for Advanced Energy Technology School of Materials Science and Engineering School of Chemistry and Chemical Engineering Shaanxi Normal University Xi’an 710119 China Dalian National Laboratory for Clean Energy iChEM Dalian Institute of Chemical Physics Chinese Academy of Sciences Dalian China

Correction for ‘Zero-thermal-quenching and photoluminescence tuning with the assistance of carriers from defect cluster traps’ by Yali Chen et al., J. Mater. Chem. C, 2018, 6, 10687–10692.

Correction for ‘Zero-thermal-quenching and photoluminescence tuning with the assistance of carriers from defect cluster traps’ by Yali Chen et al., J. Mater. Chem. C, 2018, 6, 10687–10692.

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Effects of incident energy and angle on carbon cluster ions implantation on silicon substrate:a molecular dynamics study

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Journal of Semiconductors 2017年第9期38卷 8-13页

作者： Ye Wei Shengbo Sang Bing Zhou Xiao Deng Jing Chai Jianlong Ji Yang Ge Yuanliang Huo Wendong Zhang Micro-Nano System Research Center Key Laboratory of Advanced Transducers and Intelligent Control SystemCollege of Information EngineeringTaiyuan University of TechnologyTaiyuan 030024China Research Institute of Surface Engineering Taiyuan University of TechnologyTaiyuan 030024China College of Physics and Optoelectronics Taiyuan University of TechnologyTaiyuan 030024China

Carbon cluster ion implantation is an important technique in fabricating functional devices at mi- cro/nanoscale. In this work, a numerical model is constructed for implantation and implemented with a cutting- edge molecular dynamics method. A series of simulations with varying incident energies and incident angles is performed for incidence on silicon substrate and correlated effects are compared in detail. Meanwhile, the behav- ior of the cluster during implantation is also examined under elevated temperatures. By mapping the nanoscopic morphology with variable parameters, numerical formalism is proposed to explain the different impacts on phrase transition and surface pattern formation. Particularly, implantation efficiency （IE） is computed and further used to evaluate the performance of the overall process. The calculated results could be properly adopted as the theoretical basis for designing nano-structures and adjusting devices＇ properties.

关键词： implantation low incident energies irradiation molecular dynamics

Dynamic formation of quasicondensate and spontaneous vortices in a strongly interacting Fermi gas

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arXiv 2019年

作者： Liu, Xiang-Pei Yao, Xing-Can Deng, Youjin Wang, Yu-Xuan Wang, Xiao-Qiong Li, Xiaopeng Chen, Qijin Chen, Yu-Ao Pan, Jian-Wei Hefei National Laboratory for Physical Sciences at the Microscale Department of Modern Physics University of Science and Technology of China Hefei230026 China Shanghai Branch CAS Center for Excellence in Quantum Information and Quantum Physics University of Science and Technology of China Shanghai201315 China Shanghai Research Center for Quantum Sciences Shanghai201315 China State Key Laboratory of Surface Physics Institute of Nanoelectronics and Quantum Computing Department of Physics Fudan University Shanghai200433 China Collaborative Innovation Center of Advanced Microstructures Nanjing210093 China MinJiang Collaborative Center for Theoretical Physics College of Physics and Electronic Information Engineering Minjiang University Fuzhou350108 China

We report an experimental study of quench dynamics across the superfluid transition temperature Tc in a strongly interacting Fermi gas by ramping down the trapping potential. The nonzero quasi-condensate number N0 at temperature significantly above Tc in the unitary and the BEC regimes reveals the pseudogap physics. Below Tc, a rapid growth of N0 is accompanied by spontaneous generation of tens of vortices. We observe a power law scaling of the vortex density versus the quasi-condensate formation time, consistent with the Kibble-Zurek theory. Our work provides an example of studying emerged many-body physics by quench dynamics and paves the way for studying the quantum turbulence in a strongly interacting Fermi gas. Copyright © 2019, The Authors. All rights reserved.

关键词： Electron gas