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Topological phase transitions driven by next-nearest-neighbor hopping in noncentrosymmetric cold fermi gases

Chinese Physics B 2015年第3期24卷 66-71页

作者：王瑞张存喜计青山 Department of Electronic Information Science and Engineering Zhejiang Ocean University National Laboratory of Solid State Microstructures and Department of Physics Nanjing University

We investigate the topological phase marked by the Thouless–Kohmoto–Nightingale–Nijs（TKNN） number and the phase transitions driven by the next nearest neighbor（NNN） hopping in noncentrosymmetric cold fermi gases, both spinsinglet pairing and spin-triplet pairing are considered. There exists a critical t＇c for the NNN hopping, at which the quantum phase transition occurs, and the system changes from an Abelian（non-Abelian） phase to a non-Abelian（Abelian） one. By numerically diagonalizing the Hamiltonian in the real space, the energy spectra with edge states for different topological phases and the Majorana zero modes are discussed. Although the spin-triplet pairing does not contribute to the gap closing and the phase diagram, it induces gapless states in the presence of a magnetic field, and the TKNN number in this region is still zero.

关键词： topological phase transition fermi gases Majorana fermion

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Spin-orbit coupling in Bose-Einstein condensate and degenerate fermi gases

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Frontiers of physics 2014年第5期9卷 598-612页

作者： Peng-Jun Wang Jing Zhang State Key Laboratory of Quantum Optics and Quantum Optics Devices Institute of Opto-Electronics Shanxi University Taiyuan 030006 China

We review our recent experimental realization and investigation of a spin orbit （SO） coupled Bose Einstein condensate （BEC） and quantum degenerate fermi gas. By using two counter-propagathlg Ranlan lasers and controlling the different frequency of two R,aman lasers to engineer the atom light interaction, we first study the SO coupling in BEC. Then we study SO coupling in fermi gas. We, observe the spin dephasing in spin dynamics and momentum distribution asymmetry of the equilibrium state as halhnarks of SO coupling in a fermi gas. To clearly reveal the, property of SO coupling fermi gas, we also study the momentmn-resolved radio-frequency spectroscopy which characterizes the energy momentum dispersion and spin composition of the quantum states. We observe the change of errmion surfaces in different helieity branches with different atomic density, which indicates that a Lifshitz transition of the fermi surface topology change can be found by further cooling the system. At last, we study the momentum-resolved Raman spectroscopy of an ultracoht fermi gas.

关键词： spin-orbit coupling Bose Einstein condensate fermi gases topological change momentum-resolved radio-frequency spectroscopy momentum-resolved Raman spectroscopy

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超越旋波近似的自旋轨道耦合拓扑费米子

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Science Bulletin 2024年第6期69卷 747-755页

作者：张涵王文伟乔畅张龙梁明诚吴瑞王旭杰刘雄军张熙博 International Center for Quantum Materials School of PhysicsPeking UniversityBeijing 100871China Collaborative Innovation Center of Quantum Matter Beijing 100871China School of Physics and Institute for Quantum Science and Engineering Huazhong University of Science and TechnologyWuhan 430074China Hefei National Laboratory Hefei 230088China Beijing Academy of Quantum Information Sciences Beijing 100193China International Quantum Academy Shenzhen 518048China

The realization of spin-orbit-coupled ultracold gases has driven a wide range of research and is typically based on the rotating wave approximation(RWA).By neglecting the counter-rotating terms,RWA characterizes a single near-resonant spin-orbit(SO)coupling in a two-level ***,we propose and experimentally realize a new scheme for achieving a pair of two-dimensional(2D)SO couplings for ultracold fermions beyond *** work not only realizes the first anomalous Floquet topological fermi gas beyond RWA,but also significantly improves the lifetime of the 2D-SO-coupled fermi *** on pump-probe quench measurements,we observe a deterministic phase relation between two sets of SO couplings,which is characteristic of our beyond-RWA scheme and enables the two SO couplings to be simultaneously tuned to the optimum 2D *** observe intriguing band topology by measuring two-ring band-inversion surfaces,quantitatively consistent with a Floquet topological fermi gas in the regime of high Chern *** study can open an avenue to explore exotic SO physics and anomalous topological states based on long-lived SO-coupled ultracold fermions.

关键词： Spin-orbit coupling Ultracold atoms fermi gases Quantum simulation Topological phases of matter

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