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arXiv 2019年

作者： Wang, Hui He, Yu-Ming Chung, Tung Hsun Hu, Hai Yu, Ying Chen, Si Ding, Xing Chen, Ming-Cheng Qin, Jian Yang, Xiaoxia Liu, Run-Ze Duan, Zhao-Chen Li, Jin-Peng Gerhardt, Stefan Winkler, Karol Jurkat, J. Wang, Lin-Jun Gregersen, Niels Huo, Yong-Heng Dai, Qing Yu, Siyuan Höfling, Sven Lu, Chao-Yang Pan, Jian-Wei Shanghai branch National Laboratory for Physical Sciences at Microscale Department of Modern Physics University of Science and Technology of China Shanghai201315 China CAS Centre for Excellence Synergetic Innovation Centre in Quantum Information and Quantum Physics University of Science and Technology of China Hefei Anhui230026 China Nanophotonics Research Division CAS Center for Excellence in Nanoscience National Center for Nanoscience and Technology Beijing100190 China State Key Laboratory of Optoelectronic Materials and Technologies School of Electronics and Information Technology Sun Yat-sen University Guangzhou510275 China Technische Physik Physikalisches Instität and Wilhelm Conrad Röntgen-Center for Complex Material Systems Universitat Würzburg Am Hubland WürzburgD-97074 Germany DTU Fotonik Department of Photonics Engineering Technical University of Denmark Ørsteds Plads 343 Kongens LyngbyDK-2800 Denmark SUPA School of Physics and Astronomy University of St. Andrews St. AndrewsKY16 9SS United Kingdom

An optimal single-photon source should deterministically deliver one and only one photon at a time, with no trade-off between the source’s efficiency and the photon indistinguishability. However, all reported solid-state sources of indistinguishable single photons had to rely on polarization filtering which reduced the efficiency by 50%, which fundamentally limited the scaling of photonic quantum technologies. Here, we overcome this final long-standing challenge by coherently driving quantum dots deterministically coupled to polarization-selective Purcell microcavities—two examples are narrowband, elliptical micropillars and broadband, elliptical Bragg gratings. A polarization-orthogonal excitation-collection scheme is designed to minimize the polarization-filtering loss under resonant excitation. We demonstrate a polarized single-photon efficiency of 0.60(2), a single-photon purity of 0.991(3), and an indistinguishability of 0.973(5). Our work provides promising solutions for truly optimal single-photon sources combining near-unity indistinguishability and near-unity system efficiency simultaneously. Copyright © 2019, The Authors. All rights reserved.

关键词： Particle beams

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Effect of strain on magnetic and orbital ordering of LaSrCrO3/LaSrMnO3 heterostructures

arXiv

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arXiv 2019年

作者： Koohfar, Sanaz Georgescu, Alexandru B. Hallsteinsen, Ingrid Sachan, Ritesh Roldan, Manuel A. Arenholz, Elke Kumah, Divine P. Department of Physics North Carolina State University RaleighNC27695 United States Center for Computational Quantum Physics Flatiron Institute 162 5th Avenue New YorkNY10010 United States Department of Electronic Systems Norwegian University of Science and Technology TrondheimN-7491 Norway Lawrence Berkeley National Laboratory BerkeleyCA94720 United States Mechanical and Aerospace Engineering Oklahoma State University StillwaterOK74078 United States Eyring Materials Center Arizona State University AZ85287 United States Lawrence Berkeley National Laboratory BerkeleyCA United States Cornell High Energy Synchrotron Source IthacaNY United States

We investigate the effect of strain and film thickness on the orbital and magnetic properties of LaSrCrO3 (LSCO)/LaSrMnO3 (LSMO) heterostructures using bulk magnetometry, soft X-ray magnetic spectroscopy, first-principles density functional theory, high-resolution electron microscopy and X-ray diffraction. We observe an anti-parallel ordering of the magnetic moments between the ferromagnetic LSMO layers and the LSCO spacers leading to a strain-independent ferromagnetic ground state of the LSCO/LSMO heterostructures for LSMO layers as thin as 2 unit cells. As the LSMO thickness is increased, a net ferromagnetic state is maintained, however, the average magnetic moment per Mn is found to be dependent on the magnitude of the substrate-induced strain. The differences in the magnetic responses are related to preferential occupation of the Mn x2−y2 (in-plane) d-orbitals for tensile strain and 3z2−r2 (out-of-plane) orbitals under compressive strain leading to competing ferromagnetic and anti-ferromagnetic exchange interactions within the LSMO layers. These results underscore the relative contributions of orbital, structural and spin degree of freedom and their tunability in atomically-thin crystalline complex oxide layers. Copyright © 2019, The Authors. All rights reserved.

关键词： Lanthanum compounds

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Switchable topological edge states in next-nearest-neighbour coupled resonator lattices

Switchable topological edge states in next-nearest-neighbour...

引用

Conference on Lasers and Electro-Optics/Pacific Rim, CLEOPR 2018

作者： Leykam, D. Mittal, S. Hafezi, M. Chong, Y.D. Center for Theoretical Physics of Complex Systems Institute for Basic Science Daejeon Korea Republic of Joint Quantum Institute NIST/University of Maryland College ParkMD United States Department of Electrical and Computer Engineering IREAP University of Maryland College ParkMD United States School of Physical and Mathematical Sciences Nanyang Technological University Singapore Centre for Disruptive Photonic Technologies Nanyang Technological University Singapore

We find that next-nearest-neighbour coupling in ring resonator lattices induces topological transitions and one-way edge modes. We design topological waveguides that are easily switchable using thermal, electro-optic,... 详细信息

ISBN: (纸本)9781943580453

关键词： Topology

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Probabilistic teleportation of a quantum dot spin qubit

arXiv

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arXiv 2020年

作者： Kojima, Yohei Nakajima, T. Noiri, A. Yoneda, J. Otsuka, T. Takeda, K. Li, S. Bartlett, S.D. Ludwig, A. Wieck, A.D. Tarucha, S. Department of Applied Physics University of Tokyo 7-3-1 Hongo TokyoBunkyo-ku113-8656 Japan SaitamaWako-shi351-0198 Japan Centre for Engineered Quantum Systems University of Sydney SydneyNSW2006 Australia Lehrstuhl für Angewandte Festkörperphysik Ruhr-Universität Bochum BochumD-44780 Germany School of Electrical Engineering and Telecommunications University of New South Wales SydneyNSW2052 Australia Research Institute of Electrical Communication Tohoku University 2-1-1 Katahira Aoba-ku Sendai980-8577 Japan Center for Spintronics Research Network Tohoku University 2-1-1 Katahira SendaiAoba-ku980-8577 Japan Center for Science and Innovation in Spintronics Tohoku University 2-1-1 Katahira SendaiAoba-ku980-8577 Japan

Electron spins in semiconductor quantum dots have been intensively studied for implementing quantum computation and high-fidelity single- and two-qubit operations have recently been achieved. quantum teleportation is a three-qubit protocol exploiting quantum entanglement and it serves as an essential primitive for more sophisticated quantum algorithms. Here, we demonstrate a scheme for quantum teleportation based on direct Bell measurement for a single electron spin qubit in a triple quantum dot utilizing the Pauli exclusion principle to create and detect maximally entangled states. The single spin polarization is teleported from the input qubit to the output qubit with a fidelity of 0.91. We find this fidelity is primarily limited by singlet-triplet mixing, which can be improved by optimizing the device parameters. Our results may be extended to quantum algorithms with a larger number of semiconductor spin qubits. © 2020, CC-BY.

关键词： Semiconductor quantum dots

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Mapping twisted light into and out of a photonic chip

arXiv

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arXiv 2018年

作者： Chen, Yuan Gao, Jun Jiao, Zhi-Qiang Sun, Ke Shen, Wei-Guan Qiao, Lu-Feng Tang, Hao Lin, Xiao-Feng Jin, Xian-Min State Key Laboratory of Advanced Optical Communication Systems and Networks School of Physics and Astronomy Shanghai Jiao Tong University Shanghai200240 China Institute for Quantum Science and Engineering Department of Physics Southern University of Science and Technology Shenzhen518055 China Synergetic Innovation Center of Quantum Information and Quantum Physics University of Science and Technology of China Hefei Anhui230026 China Institute of Natural Sciences Shanghai Jiao Tong University Shanghai200240 China

Twisted light carrying orbital angular momentum (OAM) provides an additional degree of freedom for modern optics and an emerging resource for both classical and quantum information technologies. Its inherently infinite dimensions can potentially be exploited by using mode multiplexing to enhance data capacity for sustaining the unprecedented growth in big data and internet traffic, and can be encoded to build large-scale quantum computing machines in high-dimensional Hilbert space. While the emission of twisted light from the surface of integrated devices to free space has been widely investigated, the transmission and processing inside a photonic chip remain to be addressed. Here, we present the first laser-direct-written waveguide being capable of supporting OAM modes and experimentally demonstrate a faithful mapping of twisted light into and out of a photonic chip. The states OAM0, OAM-1, OAM+1 and their superpositions can transmit through the photonic chip with a total efficiency up to 60% with minimal crosstalk. In addition, we present the transmission of quantum twisted light states of single photons and measure the output states with single-photon imaging. Our results may add OAM as a new degree of freedom to be transmitted and manipulated in a photonic chip for high-capacity communication and high-dimensional quantum information processing. Copyright © 2018, The Authors. All rights reserved.

关键词： Light

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Monolayer Mg2C: Negative Poisson's ratio and unconventional two-dimensional emergent fermions

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Physical Review Materials 2018年第10期2卷 104003-104003页

作者： Shan-Shan Wang Ying Liu Zhi-Ming Yu Xian-Lei Sheng Liyan Zhu Shan Guan Shengyuan A. Yang Research Laboratory for Quantum Materials Singapore University of Technology and Design Singapore 487372 Singapore Department of Applied Physics Key Laboratory of Micro-nano Measurement-Manipulation and Physics (Ministry of Education) Beihang University Beijing 100191 China School of Physics and Electronic & Electrical Engineering and Jiangsu Key Laboratory of Modern Measurement Technology and Intelligent Systems Huaiyin Normal University Huai'an Jiangsu 223300 China State Key Laboratory of Superlattices and Microstructures Institute of Semiconductors Chinese Academy of Sciences Beijing 100083 China Center for Quantum Transport and Thermal Energy Science School of Physics and Technology Nanjing Normal University Nanjing 210023 China

Two-dimensional (2D) emergent fermions and negative Poisson's ratio in 2D materials are fascinating subjects of research. Here, based on first-principles calculations and theoretical analysis, we predict that the hexacoordinated Mg2C monolayer hosts both exotic properties. We analyze its phonon spectrum, reveal the Raman-active modes, and show that it has small in-plane stiffness constants. Particularly, under the tensile strain in the zigzag direction, the Mg2C monolayer shows an intrinsic negative Poisson's ratio ∼−0.023, stemming from its unique puckered hinge structure. The material is metallic at its equilibrium state. A moderate biaxial strain can induce a metal-semimetal-semiconductor phase transition, during which several types of 2D unconventional fermions emerge, including the anisotropic Dirac fermions around 12 tilted Dirac points in the metallic phase, the 2D double Weyl fermions in the semimetal phase where the conduction and valence bands touch quadratically at a single Fermi point, and the 2D pseudospin-1 fermions at the critical point of the semimetal-semiconductor phase transition where three bands cross at a single point on the Fermi level. In addition, uniaxial strains along the high-symmetry directions break the threefold rotational symmetry and reduce the number of Dirac points. Interestingly, it also generates 2D type-II Dirac points. We construct effective models to characterize the properties of these fermions. Our result reveals Mg2C monolayer as an intriguing platform for the study of 2D unconventional fermions, and also suggests its great potential for nanoscale device applications.

关键词： Poisson ratio 2-dimensional systems Topological materials First-principles calculations

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Correlation between Dzyaloshinskii-Moriya interaction and spin mixing conductance at antiferromagnet / ferromagnet interface

arXiv

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arXiv 2018年

作者： Ma, Xin Yu, Guoqiang Razavi, Seyed A. Chang, Liang Deng, Lei Chu, Zhaodong He, Congli Wang, Kang L. Li, Xiaoqin Department of Electrical and Computer Engineering University of California Santa BarbaraCA93106 United States Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing100190 China Department of Electrical Engineering University of California Los AngelesCA90095 United States Department of Physics Center for Complex Quantum systems University of Texas at Austin AustinTX78712 United States Department of Physics University of California Los AngelesCA90095 United States

The rich interaction phenomena at antiferromagnet (AFM)/ ferromagnet (FM) interfaces are key ingredients in AFM spintronics, where many underlying mechanisms remain unclear. Here we report a correlation observed between interfacial Dzyaloshinskii-Moriya interaction (DMI) DS and effective spin mixing conductance geff←↓ at IrMn/CoFeB interface. Both DS and geff←↓ are quantitatively determined with Brillouin light scattering measurements, and increase with IrMn thickness in the range of 2.5-7.5 nm. Such correlation likely originates from the AFM-states-mediated spin-flip transitions in FM, which promote both interfacial DMI and spin pumping effect. Our findings provide deeper insight into the AFM-FM interfacial coupling for future spintronic design. Copyright © 2018, The Authors. All rights reserved.

关键词： Binary alloys

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Reconfigurable Topological Phases in Next-Nearest-Neighbor Coupled Resonator Lattices

引用

Physical Review Letters 2018年第2期121卷 023901-023901页

作者： Daniel Leykam S. Mittal M. Hafezi Y. D. Chong Center for Theoretical Physics of Complex Systems Institute for Basic Science (IBS) Daejeon 34126 Republic of Korea Joint Quantum Institute NIST/University of Maryland College Park Maryland 20742 USA Department of Electrical and Computer Engineering and IREAP University of Maryland College Park Maryland 20742 USA Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University Singapore 637371 Singapore Centre for Disruptive Photonic Technologies Nanyang Technological University Singapore 637371 Singapore

We present a reconfigurable topological photonic system consisting of a 2D lattice of coupled ring resonators, with two sublattices of site rings coupled by link rings, which can be accurately described by a tight-binding model. Unlike previous coupled-ring topological models, the design is translationally invariant, similar to the Haldane model, and the nontrivial topology is a result of next-nearest couplings with nonzero staggered phases. The system exhibits a topological phase transition between trivial and spin Chern insulator phases when the sublattices are frequency detuned. Such topological phase transitions can be easily induced by thermal or electro-optic modulators, or nonlinear cross phase modulation. We use this lattice to design reconfigurable topological waveguides, with potential applications in on-chip photon routing and switching.

关键词： Topological effects in photonic systems

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A hybrid quantum memory enabled network at room temperature

arXiv

引用

arXiv 2018年

作者： Pang, Xiao-Ling Yang, Ai-Lin Dou, Jian-Peng Li, Hang Zhang, Chao-Ni Poem, Eilon Saunders, Dylan J. Tang, Hao Nunn, Joshua Walmsley, Ian A. Jin, Xian-Min School of Physics and Astronomy Shanghai Jiao Tong University Shanghai200240 China Synergetic Innovation Center of Quantum Information and Quantum Physics University of Science and Technology of China Hefei Anhui230026 China Clarendon Laboratory University of Oxford Parks Road OxfordOX1 3PU United Kingdom Department of Physics of Complex Systems Weizmann Institute of Science Rehovot7610001 Israel Centre for Photonics and Photonic Materials Department of Physics University of Bath Claverton Down BathBA2 7AY United Kingdom Institute for Quantum Science and Engineering Department of Physics Southern University of Science and Technology Shenzhen518055 China

Teaser: Building quantum network with roomtemperature atomic and all-optical memories for scalable quantum information processing. quantum memory capable of storage and retrieval of flying photons on demand is crucial for developing quantum information technologies. However, the devices needed for long-distance links are quite different from those envisioned for local processing. Here, we present the first hybrid quantum memory enabled network by demonstrating the interconnection and simultaneous operation of two types of quantum memory: an atomic-ensemble-based memory and an all-optical loop memory. The former generates and stores single atomic excitations that can then be converted to single photons;and the latter maps incoming photons in and out on demand, at room-temperature and with a broad acceptance bandwidth. Interfacing these two types of quantum memories, we observe a well-preserved quantum cross-correlation, reaching a value of 22, and a violation of the Cauchy-Schwarz inequality up to 549 standard deviations. Furthermore, we demonstrate the creation and storage of a fully operable heralded photon chain state that can achieve memory-built-in combining, swapping, splitting, tuning and chopping single photons in a chain temporally. Such a quantum network allows atomic excitations to be generated, stored, and converted to broadband photons, which are then transferred to the next node, stored, and faithfully retrieved, all at high speed and in a programmable fashion. Copyright © 2018, The Authors. All rights reserved.

关键词： Photons

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Fast spin exchange between two distant quantum dots

arXiv

引用

arXiv 2018年

作者： Malinowski, Filip K. Martins, Frederico Smith, Thomas B. Bartlett, Stephen D. Doherty, Andrew C. Nissen, Peter D. Fallahi, Saeed Gardner, Geoffrey C. Manfra, Michael J. Marcus, Charles M. Kuemmeth, Ferdinand Center for Quantum Devices and Station Q Copenhagen Niels Bohr Institute University of Copenhagen Copenhagen2100 Denmark Centre for Engineered Quantum Systems School of Physics University of Sydney SydneyNSW2006 Australia Department of Physics and Astronomy Station Q Purdue Birck Nanotechnology Center Purdue University West LafayetteIN47907 United States School of Electrical and Computer Engineering School of Materials Engineering Purdue University West LafayetteIN47907 United States

The Heisenberg exchange interaction between neighboring quantum dots allows precise voltage control over spin dynamics, due to the ability to precisely control the overlap of orbital wavefunctions by gate electrodes. This allows the study of fundamental electronic phenomena1-4and finds applications in quantum information processing5. Although spin-based quantum circuits based on short-range exchange interactions are possible6,7, the development of scalable, longer-range coupling schemes constitutes a critical challenge within the spin-qubit community. Approaches based on capacitative coupling8 and cavity-mediated interactions9-11effectively couple spin qubits12,13to the charge degree of freedom14,15, making them susceptible to electrically-induced decoherence. The alternative is to extend the range of the Heisenberg exchange interaction by means of a quantum mediator16-19. Here, we show that a multielectron quantum dot with 50-100 electrons serves as an excellent mediator, preserving speed and coherence of the resulting spin-spin coupling while providing several functionalities that are of practical importance. These include speed (mediated two-qubit rates up to several gigahertz), distance (of order of a micrometer), voltage control, possibility of sweet spot operation20,21(reducing susceptibility to charge noise), and reversal of the interaction sign (useful for dynamical decoupling from noise)4,22,23. Copyright © 2018, The Authors. All rights reserved.

关键词： Semiconductor quantum dots

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