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Revealing the frequency-dependent oscillations in the nonlinear terahertz response induced by the Josephson current

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National Science Review 2023年第11期10卷 110-117页

作者： Sijie Zhang Zhiyuan Sun Qiaomei Liu Zixiao Wang Qiong Wu Li Yue Shuxiang Xu Tianchen Hu Rongsheng Li Xinyu Zhou Jiayu Yuan Genda Gu Tao Dong Nanlin Wang International center for quantum Materials School of PhysicsPeking University State Key Laboratory of Low-Dimensional quantum physics and Department of physics Tsinghua University Condensed Matter physics and Materials Science Department Brookhaven National Lab Beijing Academy of quantum Information sciences

Nonlinear responses of superconductors to intense terahertz radiation has been an active research *** terahertz pump-terahertz probe spectroscopy, we investigate the c-axis nonlinear optical response of a high-temperature superconducting cuprate. After excitation by a single-cycle terahertz pump pulse, the reflectivity of the probe pulse oscillates as the pump-probe delay is varied. Interestingly, the oscillatory central frequency scales linearly with the probe frequency, a fact widely overlooked in pump-probe experiments. By theoretically solving the nonlinear optical reflection problem on the interface, we show that our observation is well explained by the Josephson-type third-order nonlinear electrodynamics, together with the emission coefficient from inside the material into free space. The latter results in a strong enhancement of the emitted signal whose physical frequency is around the Josephson plasma edge. Our result offers a benchmark for and new insights into strong-field terahertz spectroscopy of related quantum materials.

关键词： high-temperature superconducting cuprates nonlinear optics time-domain tarahertz

Controllable Majorana vortex states in iron-based superconducting nanowires

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National Science Review 2022年第9期9卷 195-203页

作者： Chuang Li Xun-Jiang Luo Li Chen Dong E.Liu Fu-Chun Zhang Xin Liu School of physics and Institute for quantum Science and Engineering Huazhong University of Science and Technology Wuhan National High Magnetic Field center and Hubei Key Laboratory of Gravitation and quantum physics State Key Laboratory of Low Dimensional quantum physics Department of Physics Tsinghua University Kavli Institute for Theoretical sciences and CAS center for Excellence in Topological quantum Computing University of Chinese Academy of Sciences Collaborative Innovation center of Advanced Microstructures Nanjing University

To reve al the non-Abelian braiding statistics of Major ana zero modes(MZMs),it is crucial to design a Majorana platform,in which MZMs can be easily manipulated in a broad topological nontrivial parameter *** is also an essential step to confirm their *** this study,we propose an iron-based superconducting nanowire system with Majorana vortex states to satisfy desirable *** system has a radius-induced topological phase transition,giving a lower bound for the nanowire *** the topological phase,the iron-based superconducting nanowires have only one pair of MZMs over a wide range of radii,chemical potential and external magnetic *** wave function of MZMs has a sizable distribution at the side edge of the *** property enables the control of the interaction of MZMs in neighboring vortex nanowires and paves the way for Majorana fusion and braiding.

关键词： iron-based superconductor topological phase transition superconducting vortex Majorana zero modes nanowire

Experimental Realization of Degenerate Fermi Gases of ^(87)Sr Atoms with 10 or Two Spin Components

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Chinese physics Letters 2019年第9期36卷 18-22页

作者： Wei Qi Ming-Cheng Liang Han Zhang Yu-Dong Wei Wen-Wei Wang Xu-Jie Wang Xibo Zhang International center for quantum Materials School of PhysicsPeking UniversityBeijing 100871 Collaborative Innovation center of quantum Matter Beijing 100871 Beijing Academy of quantum Information sciences Beijing 100193

We report the experimental realization of quantum degenerate Fermi gases of87Sr atoms under controlled 10-and dual-nuclear-spin *** on laser cooling and evaporative cooling,we achieve an ultracold Fermi gas of 10^(5)atoms equally distributed over 10 spin states,with a temperature of T/T_(F)=*** further prepare a dual-spin gas by optically pumping atoms to the m_(F)=9/2 and m_(F)=7/2 states and observe a slightly lower T/T_(F)than that for a 10-spin gas under the same trapping condition,showing efficient evaporative cooling under a decreasing number N of spin states(N≥2)despite the increasing importance of Pauli *** that rethermalization becomes less efficient with N approaching unity,we evaporatively cool an almost polarized gas to 130 *** simple and efficient preparation of ultracold Fermi gases of^(87)Sr with tunable spin configurations provides a first step towards engineering topological quantum systems.

关键词： Atoms

Radiokrypton dating coming of age

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National Science Review 2016年第2期3卷 172-173页

作者： Zheng-Tian Lu Hefei National Laboratory for Physical sciences at the Microscale Synergetic Innovation Center of Quantum Information & Quantum PhysicsUniversity of Science and Technology of China

The dream of radiokrypton dating began in 1969 when Heinz Hugo Loosli and Hans Oeschger of the University of Bern first detected the decay of;Rr（half-life=230 000 yr）in krypton gas extracted from air[1].This isotope is produced in the upper atmosphere by cosmic-ray-induced spallation and neutron-activation of stable *** to its long residence time（;0;yr）in the atmosphere,;Rr is uniformly

关键词： Radiokrypton dating coming of age ATA

Giant Rashba-like spin-orbit splitting with distinct spin texture in two-dimensional heterostructures

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Chinese physics B 2021年第8期30卷 485-491页

作者： Jianbao Zhu Wei Qin Wenguang Zhu Department of physics University of Science and Technology of Chinaand Key Laboratory of Strongly-Coupled Quantum Matter PhysicsChinese Academy of SciencesHefei 230026China International center for quantum Design of Functional Materials(ICQD) Hefei National Laboratory for Physical Sciences at the Microscaleand Synergetic Innovation Center of Quantum Information and Quantum PhysicsUniversity of Science and Technology of ChinaHefei 230026China

Based on first-principles density functional theory calculation,we discover a novel form of spin-orbit(SO)splitting in two-dimensional(2D)heterostructures composed of a single Bi(111)bilayer stacking with a 2D semiconducting In_(2)Se_(2) or a 2D ferroelectricα-In_(2)Se_(3) *** SO splitting has a Rashba-like but distinct spin texture in the valence band around the maximum,where the chirality of the spin texture reverses within the upper spin-split branch,in contrast to the conventional Rashba systems where the upper branch and lower branch have opposite chirality solely in the region below the band crossing *** ferroelectric nature ofα-In_(2)Se_(3) further enables the tuning of the spin texture upon the reversal of the electric polarization with the application of an external electric *** analysis based on a tight-binding model reveals that such SO splitting texture results from the interplay of complex orbital characters and substrate *** finding enriches the diversity of SO splitting systems and is also expected to promise for spintronic applications.

关键词： spin-orbit splitting two-dimensional heterostructure first-principles calculation

Machine learning potential aided structure search for low-lying candidates of Au clusters

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Chinese physics B 2022年第7期31卷 613-619页

作者： Tonghe Ying Jianbao Zhu Wenguang Zhu Department of physics University of Science and Technology of Chinaand Key Laboratory of Strongly-Coupled Quantum Matter PhysicsChinese Academy of SciencesHefei 230026China International center for quantum Design of Functional Materials(ICQD) Hefei National Laboratory for Physical Sciences at the Microscaleand Synergetic Innovation Center of Quantum Information and Quantum PhysicsUniversity of Science and Technology of ChinaHefei 230026China

A machine learning(ML)potential for Au clusters is developed through training on a dataset including several different sized *** ML potential accurately covers the whole configuration space of Au clusters in a broad size range,thus expressing a good performance in search of their global minimum energy *** on our potential,the low-lying structures of 17 different sized Au clusters are identified,which shows that small sized Au clusters tend to form planar structures while large ones are more likely to be stereo,revealing the critical size for the two-dimensional(2D)to three-dimensional(3D)structural *** calculations demonstrate that ML is indeed powerful in describing the interaction of Au atoms and provides a new paradigm on accelerating the search of structures.

关键词： machine learning potential gold cluster first-principles calculation

Interconversion of photon-phonon in a silica optomechanical microresonator

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Science China(physics,Mechanics & Astronomy) 2015年第5期58卷 64-69页

作者： DONG ChunHua SHEN Zhen ZOU ChangLing GUO GuangCan Key Laboratory of quantum Information Chinese Academy of Sciences University of Science and Technology of China Synergetic Innovation center of quantum Information and quantum physics University of Science and Technology of China

In an optomechanical resonator, the optical and mechanical excitations can be coherently converted, which induces a transparency window for a weak probe laser beam. Here, we report an experimental study of transient optomechanically induced transparency(OMIT) using the silica microsphere with the breathing modes. The transient OMIT behavior obtained are in good agreement with theoretical calculations. In addition, the coherent interconversion between optical and mechanical excitations that can be used for light storage and readout has also been studied here. Our experimental results indicate that the light storage is closely related to the process of OMIT, and the photon-phonon conversion can be further applied to optical wavelength or optical mode conversion.

关键词： cavity optomechanics optomechanically induced transparency microsphere

Modulating magnetism of nitrogen-doped zigzag graphene nanoribbons

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Chinese physics B 2014年第6期23卷 507-513页

作者：赵尚骞吕燕吕文刚梁文杰王恩哥 Institute of physics Chinese Academy of Sciences and Beijing National Laboratory for Condensed Matter Physics International center for quantum Materials School of Physics Peking University

We present a study of electronic properties of zigzag graphene nanoribbons （ZGNRs） substitutionally doped with nitrogen atoms at a single edge by first principle calculations. We find that the two edge states near the Fermi level sepa- rate due to the asymmetric nitrogen-doping. The ground states of these systems become ferromagnetic because the local magnetic moments along the undoped edges remain and those along the doped edges are suppressed. By controlling the charge-doping level, the magnetic moments of the whole ribbons are modulated. Proper charge doping leads to interest- ing half-metallic and single-edge conducting ribbons which would be helpful for designing graphene-nanoribbon-based spintronic devices in the future.

关键词： graphene nanoribbons charge doping spin-polarization spatial localization

Universal Scaling Laws in quantum-Probabilistic Machine Learning by Tensor Network: Toward Interpreting Representation and Generalization Powers

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Chinese physics Letters 2024年第12期41卷 35-45页

作者： Sheng-Chen Bai Shi-Ju Ran center for quantum physics and intelligent sciences Department of PhysicsCapital Normal UniversityBeijing 100048China

The interpretation of representations and generalization powers has been a long-standing challenge in the fields of machine learning(ML)and artificial *** study contributes to understanding the emergence of universal scaling laws in quantum-probabilistic *** consider the generative tensor network(GTN)in the form of a matrix-product state as an example and show that with an untrained GTN(such as a random TN state),the negative logarithmic likelihood(NLL)L generally increases linearly with the number of features M,that is,L≃kM+*** is a consequence of the so-called“catastrophe of orthogonality,”which states that quantum many-body states tend to become exponentially orthogonal to each other as M *** study reveals that,while gaining information through training,the linear-scaling law is suppressed by a negative quadratic correction,leading to L≃βM−αM^(2)+*** scaling coefficients exhibit logarithmic relationships with the number of training samples and quantum channelsχ.The emergence of a quadratic correction term in the NLL for the testing(training)set can be regarded as evidence of the generalization(representation)power of the ***-parameterization can be identified by the deviation in the values ofαbetween the training and testing sets while increasingχ.We further investigate how orthogonality in the quantum-feature map relates to the satisfaction of quantum-probabilistic interpretation and the representation and generalization powers of the *** universal scaling laws in quantum-probabilistic ML would be a valuable step toward establishing a white-box ML scheme interpreted within the quantum-probabilistic framework.

关键词： quantum generalization scaling