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arXiv 2020年

作者： Broadway, David A. Scholten, Sam C. Tan, Cheng Dontschuk, Nikolai Lillie, Scott E. Johnson, Brett C. Zheng, Guolin Wang, Zhenhai Oganov, Artem R. Tian, Shangjie Li, Chenghe Lei, Hechang Wang, Lan Hollenberg, Lloyd C. L. Tetienne, Jean-Philippe School of Physics University of Melbourne ParkvilleVIC3010 Australia Centre for Quantum Computation and Communication Technology School of Physics University of Melbourne ParkvilleVIC3010 Australia Department of Physics University of Basel Klingelbergstrasse 82 BaselCH-4056 Switzerland School of Science RMIT University MelbourneVIC3000 Australia Skolkovo Institute of Science and Technology Skolkovo Innovation Center 3 Nobel Street Moscow143026 Russia School of Telecommunication and Information Engineering Nanjing University of Posts and Telecommunications Nanjing Jiangsu210003 China Moscow Institute of Physics and Technology 9 Institutsky Lane Dolgoprudny Moscow Region141700 Russia International Center for Materials Discovery Northwestern Polytechnical University Xi'an710072 Department of Physics Beijing Key Laboratory of Optoelectronic Functional Materials and Micro-Nano Devices Renmin University of China Beijing100872

The recent isolation of two-dimensional van der Waals magnetic materials has uncovered rich physics that often differs from the magnetic behaviour of their bulk counterparts. However, the microscopic details of fundamental processes such as the initial magnetization or domain reversal, which govern the magnetic hysteresis, remain largely unknown in the ultrathin limit. Here we employ a widefield nitrogen-vacancy (NV) microscope to directly image these processes in few-layer akes of magnetic semiconductor vanadium triiodide (VI3). We observe complete and abrupt switching of most akes at fields Hc 0.5-1 T (at 5 K) independent of thickness down to two atomic layers, with no intermediate partially-reversed state. The coercive field decreases as the temperature approaches the Curie temperature (Tc 50 K), however, the switching remains abrupt. We then image the initial magnetization process, which reveals thickness-dependent domain wall depinning fields well below Hc. These results point to ultrathin VI3 being a nucleation-type hard ferromagnet, where the coercive field is set by the anisotropy-limited domain wall nucleation field. This work illustrates the power of widefield NV microscopy to investigate magnetization processes in van der Waals ferromagnets, which could be used to elucidate the origin of the hard ferromagnetic properties of other materials and explore field- A nd current-driven domain wall dynamics. Copyright © 2020, The Authors. All rights reserved.

关键词： Van der Waals forces

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The ρ radiative decay width from lattice QCD 9

The ρ radiative decay width from lattice QCD

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9th International Workshop on Chiral Dynamics, CD 2018

作者： Petschlies, Marcus Alexandrou, Constantia Leskovec, Luka Meinel, Stefan Rendon, Gumaro Negele, John W. Pochinsky, Andrew Paul, Srijit Syritsyn, Sergey Helmholtz-Institut für Strahlen- und Kernphysik Bonn University Germany Computation-based Science and Technology Research Center Cyprus Institute Department of Physics University of Cyprus Cyprus Jeffersion Lab United States Department of Physics University of Arizona United States Center for Theoretical Physics Laboratory for Nuclear Science Department of Physics Massachusetts Institute of Technology United States Computation-based Science and Technology Research Center Cyprus Institute Cyprus Department of Physics and Astronomy Stony Brook University United States

Pion photoproduction constitutes a prototype process, which allows for the study of the electro-weak decay of a QCD-unstable state, the ρ resonance. It is also the most straightforward process to investigate such (resonant) transition matrix elements in lattice QCD. We performed a lattice calculation of the process ππ → ρ → πγ, at presently the lightest pion mass of 317 MeV and in a large box of size (3.6 fm)3. In addition to outlining the method for our calculation, we give account of our analysis of systematic uncertainties, with focus on parametrization dependence of the P−wave phase shift and the analytic continuation of our lattice data to the ρ resonance pole to extract the coupling |Gρπγ | = 0.0802 (38). © Copyright owned by the author(s) under the terms of the Creative Commons.

关键词： Uncertainty analysis

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Why Are There Six Degrees of Separation in a Social Network?

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Physical Review X 2023年第2期13卷 021032-021032页

作者： I. Samoylenko D. Aleja E. Primo K. Alfaro-Bittner E. Vasilyeva K. Kovalenko D. Musatov A. M. Raigorodskii R. Criado M. Romance D. Papo M. Perc B. Barzel S. Boccaletti Moscow Institute of Physics and Technology 9 Institutskiy Pereulok Dolgoprudny Moscow Region 141701 Russia National Research University Higher School of Economics 6 Ulitsa Usacheva Moscow 119048 Russia Universidad Rey Juan Carlos Calle Tulipán s/n 28933 Móstoles Madrid Spain Department of Internal Medicine University of Michigan Ann Arbor Michigan 48109 USA Laboratory of Mathematical Computation on Complex Networks and their Applications Universidad Rey Juan Carlos Calle Tulipán s/n Móstoles 28933 Madrid Spain P.N. Lebedev Physical Institute of the Russian Academy of Sciences 53 Leninsky Prospekt Moscow 119991 Russia Scuola Superiore Meridionale Largo S. Marcellino 10 80138 Napoli NA Italy Russian Academy of National Economy and Public Administration 84 Prospekt Vernadskogo Moscow 119606 Russia Caucasus Mathematical Center at Adyghe State University 208 Pervomayskaya Ulitsa Maykop Adygea 385000 Russia Moscow State University 1 Leninskie Gory Moscow 119991 Russia Institute of Mathematics and Computer Science Buryat State University 5 Ulitsa Ranzhurova Ulan-Ude Buryatia 670000 Russia Data Complex Networks and Cybersecurity Research Institute Universidad Rey Juan Carlos Plaza Manuel Becerra 14 28028 Madrid Spain Department of Neuroscience and Rehabilitation University of Ferrara Ferrara Italy Center for Translational Neurophysiology of Speech and Communication Fondazione Istituto Italiano di Tecnologia Ferrara Italy Faculty of Natural Sciences and Mathematics University of Maribor Koroška cesta 160 2000 Maribor Slovenia Department of Medical Research China Medical University Hospital China Medical University Taichung 404332 Taiwan Complexity Science Hub Vienna Josefstädterstraße 39 1080 Vienna Austria Alma Mater Europaea Slovenska ulica 17 2000 Maribor Slovenia Department of Physics Kyung Hee University 26 Kyungheedae-ro Dongdaemun-gu Seoul Republic of Korea Department of Mathematics Bar-Ilan University Ramat-Gan 52900 Israel The Gonda Multi

A wealth of evidence shows that real-world networks are endowed with the small-world property, i.e., that the maximal distance between any two of their nodes scales logarithmically rather than linearly with their size. In addition, most social networks are organized so that no individual is more than six connections apart from any other, an empirical regularity known as the six degrees of separation. Why social networks have this ultrasmall-world organization, whereby the graph’s diameter is independent of the network size over several orders of magnitude, is still unknown. We show that the “six degrees of separation” is the property featured by the equilibrium state of any network where individuals weigh between their aspiration to improve their centrality and the costs incurred in forming and maintaining connections. We show, moreover, that the emergence of such a regularity is compatible with all other features, such as clustering and scale-freeness, that normally characterize the structure of social networks. Thus, our results show how simple evolutionary rules of the kind traditionally associated with human cooperation and altruism can also account for the emergence of one of the most intriguing attributes of social networks.

关键词： Degree distributions Network evolution Real world networks Small-world networks

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Ferromagnetic induced Kondo effect in graphene with a magnetic impurity

arXiv

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arXiv 2020年

作者： Li, Gao-Yang Fang, Tie-Feng Guo, Ai-Min Sun, Qing-Feng School of Physical Science and Technology Lanzhou University Lanzhou730000 China Hunan Key Laboratory for Super-microstructure and Ultrafast Process School of Physics and Electronics Central South University Changsha410083 China International Center for Quantum Materials School of Physics Peking University Beijing100871 China Collaborative Innovation Center of Quantum Matter Beijing100871 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing100190 China

We investigate the many-body effects of a magnetic adatom in ferromagnetic graphene by using the numerical renormalization group method. The nontrivial band dispersion of ferromagnetic graphene gives rise to interesting Kondo physics different from that in conventional ferromagnetic materials. For a half-filled impurity in undoped graphene, the presence of ferromagnetism can bring forth Kondo correlations, yielding two kink structures in the local spectral function near the Fermi energy. When the spin splitting of local occupations is compensated by an external magnetic field, the two Kondo kinks merge into a full Kondo resonance characterizing the fully screened ground state. Strikingly, we find the resulting Kondo temperature monotonically increases with the spin polarization of Dirac electrons, which violates the common sense that ferromagnetic bands are usually detrimental to Kondo correlations. Doped ferromagnetic graphene can behave as half metals, where its density of states at the Fermi energy linearly vanishes for one spin direction but keeps finite for the opposite direction. In this regime, we demonstrate an abnormal Kondo resonance that occurs in the first spin direction, while completely absent in the other one. Copyright © 2020, The Authors. All rights reserved.

关键词： Ferromagnetism

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A two-dimensional GeSe/SnSe heterostructure for high performance thin-film solar cells

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Journal of Materials Chemistry A 2019年第18期7卷 11265-11271页

作者： Yuliang Mao Congsheng Xu Jianmei Yuan Hongquan Zhao Hunan Key Laboratory for Micro-Nano Energy Materials and Devices School of Physics and Optoelectronics Xiangtan University Hunan 411105 China Hunan Key Laboratory for Computation and Simulation in Science and Engineering School of Mathematics and Computational Science Xiangtan University Hunan 411105 China Chongqing Institute of Green and Intelligent Technology Chinese Academy of Sciences Chongqing 401120 China

Based on the first-principles calculations, we demonstrated that a GeSe/SnSe heterostructure has type-II band alignment and a direct band gap, which can effectively prevent the recombination of photogenerated electron–hole pairs. Moreover, the GeSe/SnSe heterostructure also exhibits strong optical absorption intensity, which can reach the order of 10⁵ cm⁻¹. Our predicted photoelectric conversion efficiency (PCE) for the GeSe/SnSe heterostructure reaches 21.47%. We also found that the hole carrier mobility of the GeSe/SnSe heterostructure along the x direction has been significantly improved to 6.42 × 10⁴ cm² V⁻¹ s⁻¹, which is higher than that of black phosphorus (1 × 10⁴ cm² V⁻¹ s⁻¹). By applying a vertical external electric field, we found that the band gap and band offset of the GeSe/SnSe heterojunction can be effectively tuned. The revealed type-II band alignment, strong optical absorption, superior PCE and superior hole carrier mobility of the GeSe/SnSe heterostructure imply that this new proposed material has broad application prospects in solar cells.

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Experimental Validation of Quantum Steering Ellipsoids and Tests of Volume Monogamy Relations

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Physical Review Letters 2019年第7期122卷 070402-070402页

作者： Chao Zhang Shuming Cheng Li Li Qiu-Yue Liang Bi-Heng Liu Yun-Feng Huang Chuan-Feng Li Guang-Can Guo Michael J. W. Hall Howard M. Wiseman Geoff J. Pryde Key Laboratory of Quantum Information University of Science and Technology of China CAS Hefei 230026 People’s Republic of China CAS Center For Excellence in Quantum Information and Quantum Physics University of Science and Technology of China Hefei 230026 People’s Republic of China Centre for Quantum Computation and Communication Technology (Australian Research Council) Centre for Quantum Dynamics Griffith University Brisbane QLD 4111 Australia

The set of all qubit states that can be steered to by measurements on a correlated qubit is predicted to form an ellipsoid—called the quantum steering ellipsoid—in the Bloch ball. This ellipsoid provides a simple visual characterization of the initial two-qubit state, and various aspects of entanglement are reflected in its geometric properties. We experimentally verify these properties via measurements on many different polarization-entangled photonic qubit states. Moreover, for pure three-qubit states, the volumes of the two quantum steering ellipsoids generated by measurements on the first qubit are predicted to satisfy a tight monogamy relation, which is strictly stronger than the well-known monogamy of entanglement for concurrence. We experimentally verify these predictions, using polarization and path entanglement. We also show experimentally that this monogamy relation can be violated by a mixed entangled state, which nevertheless satisfies a weaker monogamy relation.

关键词： Nonlocality Quantum correlations in quantum information Quantum optics

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Simultaneous excitation of two noninteracting atoms with time-frequency correlated photon pairs in a superconducting circuit

arXiv

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arXiv 2020年

作者： Ren, Wenhui Liu, Wuxin Song, Chao Li, Hekang Guo, Qiujiang Wang, Zhen Zheng, Dongning Agarwal, Girish S. Scully, Marlan O. Zhu, Shi-Yao Wang, H. 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 Institute of Physics Chinese Academy of Sciences Bejing100190 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Bejing100190 China Institute for Quantum Science and Engineering Departments of Biological and Agricultural Engineering Physics and Astronomy Texas A&M University College StationTX77843 United States Baylor University WacoTX76706 United States

Here we report the first observation of simultaneous excitation of two noninteracting atoms by a pair of time-frequency correlated photons in a superconducting circuit. The strong coupling regime of this process enables the synthesis of a three-body interaction Hamiltonian, which allows the generation of the tripartite Greenberger-Horne-Zeilinger state in a single step with a fidelity as high as 0.95. We further demonstrate the quantum Zeno effect of inhibiting the simultaneous two-atom excitation by continuously measuring whether the first photon is emitted. This work provides a new route in synthesizing many-body interaction Hamiltonian and coherent control of entanglement. Copyright © 2020, The Authors. All rights reserved.

关键词： Hamiltonians

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Geometry of variational methods: dynamics of closed quantum systems

arXiv

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arXiv 2020年

作者： Hackl, Lucas Guaita, Tommaso Shi, Tao Haegeman, Jutho Demler, Eugene Cirac, Ignacio QMATH Department of Mathematical Sciences University of Copenhagen Universitetsparken 5 Copenhagen2100 Denmark Max-Planck-Institut für Quantenoptik Hans-Kopfermann-Str. 1 Garching85748 Germany Munich Center for Quantum Science and Technology Schellingstraße 4 München80799 Germany Munich Center for Quantum Science and Technology Schellingstr. 4 München80799 Germany CAS Key Laboratory of Theoretical Physics Institute of Theoretical Physics Chinese Academy of Sciences Beijing100190 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing100049 China Department of Physics and Astronomy Ghent University Krijgslaan 281 Gent9000 Belgium Lyman Laboratory Department of Physics Harvard University 17 Oxford St. CambridgeMA02138 United States

We present a systematic geometric framework to study closed quantum systems based on suitably chosen variational families. For the purpose of (A) real time evolution, (B) excitation spectra, (C) spectral functions and (D) imaginary time evolution, we show how the geometric approach highlights the necessity to distinguish between two classes of manifolds: Kähler and non-Kähler. Traditional variational methods typically require the variational family to be a Kähler manifold, where multiplication by the imaginary unit preserves the tangent spaces. This covers the vast majority of cases studied in the literature. However, recently proposed classes of generalized Gaussian states make it necessary to also include the non-Kähler case, which has already been encountered occasionally. We illustrate our approach in detail with a range of concrete examples where the geometric structures of the considered manifolds are particularly relevant. These go from Gaussian states and group theoretic coherent states to generalized Gaussian states. Copyright © 2020, The Authors. All rights reserved.

关键词： Group theory

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Spin-dependent electron transport along hairpin-like DNA molecules

arXiv

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arXiv 2020年

作者： Hu, Pei-Jia Wang, Si-Xian Gao, Xiao-Hui Zhang, Yan-Yang Fang, Tie-Feng Guo, Ai-Min Sun, Qing-Feng Hunan Key Laboratory for Super-microstructure and Ultrafast Process School of Physics and Electronics Central South University Changsha410083 China School of Physics and Electronic Engineering Guangzhou University Guangzhou510006 China School of Physical Science and Technology Lanzhou University Lanzhou730000 China International Center for Quantum Materials School of Physics Peking University Beijing100871 China Collaborative Innovation Center of Quantum Matter Beijing100871 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing100190 China

The chirality-induced spin selectivity (CISS), demonstrated in diverse chiral molecules by numerous experimental and theoretical groups, has been attracting extensive and ongoing interest in recent years. As the secondary structure of DNA, the charge transfer along DNA hairpins has been widely studied for more than two decades, finding that DNA hairpins exhibit spin-related effects as reported in recent experiments. Here, we propose a setup to demonstrate directly the CISS effect in DNA hairpins contacted by two nonmagnetic leads at both ends of the stem. Our results indicate that DNA hairpins present pronounced CISS effect and the spin polarization could be enhanced by using conducting molecules as the loop. In particular, DNA hairpins show several intriguing features, which are different from other chiral molecules. First, the local spin currents can flow circularly and assemble into a number of vortex clusters when the electron energy locates in the left/right electronic band of the stem. The chirality of vortex clusters in each band is the same and will be reversed by switching the electron energy from the left band to the right one, inducing the sign reversal of the spin polarization. Interestingly, the local spin currents can be greater than the corresponding spin component of the source-drain current. Second, both the conductance and the spin polarization can increase with molecular length as well as dephasing strength, contrary to the physical intuition that the transmission ability of molecular wires should be poorer when suffering from stronger scattering. Third, we unveil the optimal contact configuration of efficient electron transport and that of the CISS effect, which are distinct from each other and can be controlled by dephasing strength. The underlying physical mechanism is illustrated. Copyright © 2020, The Authors. All rights reserved.

关键词： Chirality

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Decays of Majorana or Andreev Oscillations Induced by Steplike Spin-Orbit Coupling

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Physical Review Letters 2019年第14期122卷 147701-147701页

作者： Zhan Cao Hao Zhang Hai-Feng Lü Wan-Xiu He Hai-Zhou Lu X. C. Xie Shenzhen Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and Technology Shenzhen 518055 China School of Physics Southeast University Nanjing 211189 China Peng Cheng Laboratory Shenzhen 518055 China Shenzhen Key Laboratory of Quantum Science and Engineering Shenzhen 518055 China State Key Laboratory of Low Dimensional Quantum Physics Department of Physics Tsinghua University Beijing 100084 China Beijing Academy of Quantum Information Sciences Beijing 100193 China School of Physics University of Electronic Science and Technology of China Chengdu 610054 China Center for Interdisciplinary Studies and Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education Lanzhou University Lanzhou 730000 China International Center for Quantum Materials School of Physics Peking University Beijing 100871 China CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing 100190 China

The Majorana zero mode in the semiconductor-superconductor nanowire is one of the promising candidates for topological quantum computing. Recently, in islands of nanowires, subgap-state energies have been experimentally observed to oscillate as a function of the magnetic field, showing a signature of overlapped Majorana bound states. However, the oscillation amplitude either dies away after an overshoot or decays, sharply opposite to the theoretically predicted enhanced oscillations for Majorana bound states. We reveal that a steplike distribution of spin-orbit coupling in realistic devices can induce the decaying Majorana oscillations, resulting from the coupling-induced energy repulsion between the quasiparticle spectra on the two sides of the step. This steplike spin-orbit coupling can also lead to decaying oscillations in the spectrum of the Andreev bound states. For Coulomb-blockade peaks mediated by the Majorana bound states, the peak spacings have been predicted to correlate with peak heights by a π/2 phase shift, which was ambiguous in recent experiments and may be explained by the steplike spin-orbit coupling. Our work will inspire more works to reexamine effects of the nonuniform spin-orbit coupling, which is generally present in experimental devices.

关键词： Coulomb blockade Majorana fermions Quantum transport Spin-orbit coupling Topological phases of matter Topological superconductors

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