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Chinese Physics B 2009年第2期18卷 715-725页

作者：董行马永利 Department of Physics Fudan University

Using quantum hydrodynamic approaches, we study the quantum pressure correction to the collective excitation spectrum of the interacting trapped superfluid Fermi gases in the bec-bcs crossover. Based on a phenomenological equation of state, we derive hydrodynamic equations of the system in the whole bec-bcs crossover regime. Beyond the Thomas-Fermi approximation, expressions of the frequency corrections of collective modes for both spherical and axial symmetric traps excited in the bec-bcs crossover are given explicitly. The corrections of the eigenfrequencies due to the quantum pressure and their dependence on the inverse interaction strength, anisotropic parameter and particle numbers of the condensate are discussed in detail.

关键词： bec-bcs crossover hydrodynamic approaches perturbation method

Observation of the bec-bcs crossover in a degenerate Fermi gas of lithium atoms

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Chinese Physics B 2022年第1期31卷 480-484页

作者： Xiang-Chuan Yan Da-Li Sun Lu Wang Jing Min Shi-Guo Peng Kai-Jun Jiang State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics Wuhan Institute of Physics and MathematicsInnovation Academy for Precision Measurement Science and TechnologyChinese Academy of SciencesWuhan 430071China Center for Cold Atom Physics Chinese Academy of SciencesWuhan 430071China University of Chinese Academy of Sciences Beijing 100049China

We observe characteristic atomic behaviors in the Bose-Einstein-condensation-Bardeen-Cooper-Schrieffer(bec-bcs)crossover,by accurately tuning the magnetic field across the Feshbach resonance of lithium *** magnetic field is calibrated by measuring the Zeeman shift of the optical transition.A non-monotonic anisotropic expansion is observed across the Feshbach *** density distribution is explored in different interacting regimes,where a condensate of diatomic molecules forms in the bec limit with the indication of a bimodal *** also measure the three-body recombination atom loss in the bec-bcs crossover,and find that the magnetic field of the maximum atom loss is in the bec limit and gets closer to the Feshbach resonance when decreasing the atom temperature,which agrees with previous experiments and theoretical *** work builds up a controllable platform for the study on the strongly interacting Fermi gas.

关键词： bec-bcs crossover three-body recombination anisotropic expansion

Energy Spectrum of a Degenerate Fermi Gas at the bec-bcs crossover

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Communications in Theoretical Physics 2007年第5X期48卷 855-858页

作者： FANG Yuan Beijing National Laboratory for Condensed Matter Physics Institute of Physics the Chinese Academy of Sciences Beijing 100080 China

A theoretical study of the bcs-bec crossover is presented. Starting from a two-channel Boson-Fermion resonance model, the bcs-Bogoiubov mean-field method and the Green＇s function method are adopted. The result shows that we can end up with a bcs-type theory but with a composite order parameter. Calculation shows that the Bose condensate of bcs Cooper pairs is proportional to the molecular bec of Bose molecules. The resonance superfluid phase is indicated by the energy spectrum with an obvious interpretation of the transition mechanism.

关键词： degenerate Fermi gas bec-bcs crossover Feshbach resonance

D-Dimensional Dirac Fermions bec-bcs crossover Thermodynamics

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Communications in Theoretical Physics 2007年第7期48卷 99-106页

作者： CHEN Ji-Sheng Institute of Particle Physics & Physics Department,Central China Normal University,Wuhan 430079,China Institute of Particle Physics & Physics Department Central China Normal University Wuhan 430079 China

An effective relativistic continuum massive Proca Lagrangian action is used to account for the Lorentzvector condensation effects on the equation of state of the strongly interacting fermions *** interior quantumfluctuation effects are incorporated as an external field approximation indirectly through a fictive generalized ThomsonProblem counterterm *** general analytical formulas for the d-dimensional thermodynamics are given nearthe unitary limit region,In the non-relativistic limit for d=3,the universal dimensionless coefficientε=4/9 andenergy gap △/ε_f=5/18 are reasonably consistent with the existing theoretical and experimental *** the unitarylimit for d=2 and T=0,the universal coefficient can even approach the extreme occasion ξ=0 corresponding to theinfinite effective fermion mass m~*=∞,which can be mapped to the strongly coupled two-dimensional electrons and isquite similar to the three-dimensional Bose-Einstein condensation of ideal boson ***,for d=1,the universalcoefficient ξ is negative,implying the non-existence of phase transition from superfluidity to normal *** solutionsmanifest the quantum Ising universal class characteristic of the strongly coupled unitary fermions gas.

关键词： unitary fermions thermodynamics bec-bcs crossover statistical methods

Oscillatory-like expansion of a Fermionic superfluid

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Science Bulletin 2020年第1期65卷 7-11,M0003页

作者： Xiao-Qiong Wang Yu-Ping Wu Xiang-Pei Liu Yu-Xuan Wang Hao-Ze Chen Mudassar Maraj Youjin Deng Xing-Can Yao Yu-Ao Chen Jian-Wei Pan Shanghai Branch National Laboratory for Physical Sciences at Microscale and Department of Modem PhysicsUniversity of Science and Technology of ChinaShanghai 201315China CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics University of Science and Technology of ChinaHefei 230026China

We study the expansion behaviors of a Fermionic superfluid in a cigar-shaped optical dipole trap for the whole bec-bcs crossover and various *** low temperature(0:06(1)T_F),the atom cloud undergoes an anisotropic hydrodynamic expansion over 30 ms,which behaves like oscillation in the horizontal *** analyzing the expansion dynamics according to the superfluid hydrodynamic equation,the effective polytropic index y of Equation-of-State(EoS)of Fermionic superfluid is *** y values show a non-monotonic behavior over the bec-bcs crossover,and have a good agreement with the theoretical results in the unitarity and bec *** normalized quasi-frequencies of the oscillatory expansion are measured,which drop significantly from the bec side to the bcs side and reach a minimum value of 1.73 around 1/k_Fa=-0:*** work improves the understanding of the dynamic properties of strongly interacting Fermi gas.

关键词： Fermionic superfluid Oscillatory-like expansion bec-bcs crossover Equation-of-State

基于AdS/CFT对偶的零温超流中的孤子研究

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基于AdS/CFT对偶的零温超流中的孤子研究

作者：高猛中国石油大学(北京)

学位级别：硕士

Ad S/CFT是Maldacena在1999年在弦论中首先提出的一种对偶关系,该对偶关系是指反德西特时空与边界上共形场论的等价关系,Ad S/CFT又称为全息原理。近几年以来,Ad S/CFT在凝聚态中的应用越来越广泛,主要表现为在反德西特空间中研究与引... 详细信息

Ad S/CFT是Maldacena在1999年在弦论中首先提出的一种对偶关系,该对偶关系是指反德西特时空与边界上共形场论的等价关系,Ad S/CFT又称为全息原理。近几年以来,Ad S/CFT在凝聚态中的应用越来越广泛,主要表现为在反德西特空间中研究与引力相关的物理规律,然后根据全息字典对应到边界上的凝聚态中的物理规律。本文主要是借助于Ad S/CFT来研究零温超流背景下的孤子构型,首先研究了零温超流中的物质场的均匀构型,并且计算得到了发生超流相变的临界化学势。在大于临界化学势的条件下计算了黑孤子构型以及黑孤子的准正频率,结果表明在不同量子化形式下存在两种不同类型的超流体系,即bcs-like超流和bec超流,同时发现黑孤子的静态解是不稳定的。然后,本文首次在零温全息超流中得到了以一定速度运动的灰孤子构型。因为运动的孤子要求系统没有耗散,所以需要使用最简单的零温超流模型才能得到灰孤子构型。除此之外,在标准量子化的灰孤子构型中存在一个永久的波动行为,这个波动类似于bcs极限下的费米超流中的Friedel震荡。本文实现了凝聚态中的bec-bcs交叠区域（crossover）物理图像,无论是在黑孤子还是在灰孤子构型中,标准量子化下体系对应着bcs-like超流,另一种（alternative）量子化下对应着bec-like超流。

关键词： AdS/CFT 零温全息超流 bec-bcs crossover 灰孤子 Friedel震荡