HKU Scholars Hubhttp://hub.hku.hkThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 07 Aug 2022 16:20:19 GMT2022-08-07T16:20:19Z50481- Bose-Hubbard models with staggered flux: Quantum phases, collective excitation, and tricriticalityhttp://hdl.handle.net/10722/203311Title: Bose-Hubbard models with staggered flux: Quantum phases, collective excitation, and tricriticality
Authors: Yao, J; Zhang, S
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/2033112014-01-01T00:00:00Z
- Universal properties of the ultracold Fermi gashttp://hdl.handle.net/10722/206542Title: Universal properties of the ultracold Fermi gas
Authors: Zhang, S; Leggett, AJ
Abstract: We present some general considerations on the properties of a two-component ultracold Fermi gas along the BEC-BCS crossover. It is shown that the interaction energy and the free energy can be written in terms of a single dimensionless function h (ξ,τ), where ξ=- (kF as) -1 and τ=TTF. The function h (ξ,τ) incorporates all the many-body physics and naturally occurs in other physical quantities as well. In particular, we show that the average rf-spectroscopy shift δω ̄ (ξ,τ) and the molecular fraction fc (ξ,τ) in the closed channel can be expressed in terms of h (ξ,τ) and thus have identical temperature dependence. The conclusions should have testable consequences in future experiments.
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/10722/2065422009-01-01T00:00:00Z
- Sum-rule analysis of radio-frequency spectroscopy of ultracold Fermi gashttp://hdl.handle.net/10722/206541Title: Sum-rule analysis of radio-frequency spectroscopy of ultracold Fermi gas
Authors: Zhang, S; Leggett, AJ
Abstract: We carried out an analysis based on sum rules and determined the radio-frequency spectroscopy shift observed in Chin 's experiment. It is shown that such a shift can be interpreted as spin correlations peculiar to a BCS-type state. An analytical form for the shift is obtained which enables us to make quantitative comparisons with the experiment throughout the crossover. We also calculated the width of the resonance. An interesting consequence is noticed, which can possibly be tested by future experiments.
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10722/2065412008-01-01T00:00:00Z
- Coherent Heteronuclear Spin Dynamics in an Ultracold Spinor Mixturehttp://hdl.handle.net/10722/214481Title: Coherent Heteronuclear Spin Dynamics in an Ultracold Spinor Mixture
Authors: Li, XK; Zhu, B; He, XD; Wang, FD; Guo, MY; Xu, ZF; Zhang, S; Wang, DJ
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2144812015-01-01T00:00:00Z
- BCS-BEC crossover in Haldane modelhttp://hdl.handle.net/10722/225983Title: BCS-BEC crossover in Haldane model
Authors: Zhang, Y; Xu, Z; Zhang, S
Abstract: We theoretically investigate BCS-BEC crossover in spinful Haldane model. We find there are two topologically distinct superfluidity phases which are characterized by chern number C=0 and 2, respectively. At half filling, the region of existing of the topological phase is extremely small. However, when the filling factor deviates from half-filling, the regions of topological phase become quite large. With the increasing of interaction, the topologically trival superfluid phase enters topological phase and then reenter topologically trival superfluid phase. This is because with the interaction increasing, the chemical potential displays non-monotonic behaviors. When the spatial inversion is broken, the paring gaps become different between two sublattices of honeycomb lattice. At the same time, a gapless topological superfluid phase appears. However, the region of topological superfluidity phase became smaller. Lastly, we consider Gaussian fluctuations about mean-field phases. Our results show there are two branch collective modes, one is gapless Anderson-Bogoliubov mode, and the other is gapped Leggett mode. Damping of Leggett mode reaches largest values when one approaches topological phase transition points.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/2259832011-01-01T00:00:00Z
- Mott-superfluid transition for spin-orbit-coupled bosons in one-dimensional optical latticeshttp://hdl.handle.net/10722/199206Title: Mott-superfluid transition for spin-orbit-coupled bosons in one-dimensional optical lattices
Authors: Xu, Z; Cole, WS; Zhang, S
Abstract: We study the effects of spin-orbit coupling on the Mott-superfluid transition of bosons in a one-dimensional optical lattice. We determine the strong-coupling magnetic phase diagram by a combination of exact analytic and numerical means. Smooth evolution of the magnetic structure into the superfluid phases is investigated with the density matrix renormalization group technique. Other magnetic phases are seen and phase transitions between them within the superfluid regime are discussed. Possible experimental detection is discussed.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/1992062014-01-01T00:00:00Z
- Evidence for universal relations describing a gas with <i>p</i>-wave interactionshttp://hdl.handle.net/10722/227398Title: Evidence for universal relations describing a gas with <i>p</i>-wave interactions
Authors: Luciuk, C; Trotzky, S; Smale, S; Yu, Z; Zhang, S; Thywissen, JH
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2273982016-01-01T00:00:00Z
- Proposed realization of itinerant ferromagnetism in optical latticeshttp://hdl.handle.net/10722/167076Title: Proposed realization of itinerant ferromagnetism in optical lattices
Authors: Zhang, S; Hung, HH; Wu, C
Abstract: We propose a scheme to realize the itinerant ferromagnetism of two-component cold fermionic atoms in the p-orbital bands in optical lattices. The band flatness in the two-dimensional honeycomb lattice dramatically amplifies the interaction effect, driving the ferromagnetic transition even with a relatively weak repulsive interaction. This scheme has the advantage that the stability of the system can be maintained without causing decay to the molecular state as one approaches the Feshbach resonance from the side with the positive scattering length. Experimental signatures and detections are also discussed. ©2010 The American Physical Society.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10722/1670762010-01-01T00:00:00Z
- Atom loss maximum in ultra-cold Fermi gaseshttp://hdl.handle.net/10722/167077Title: Atom loss maximum in ultra-cold Fermi gases
Authors: Zhang, S; Ho, TL
Abstract: Recent experiments on atom loss in ultra-cold Fermi gases all show a maximum at a magnetic field below Feshbach resonance, where the s-wave scattering length is large (comparable to inter-particle distance) and positive. These experiments have been performed over a wide range of conditions, with temperatures and trap depths spanning three decades. Different groups have come up with different explanations, including the emergence of Stoner ferromagnetism. Here, we show that this maximum is a consequence of two major steps. The first is the establishment of a population of shallow dimers, which is the combined effect of dimer formation through three-body recombination, and the dissociation of shallow dimers back to atoms through collisions. The dissociation process will be temperature dependent and is affected by Pauli blocking at low temperatures. The second is the relaxation of shallow dimers into tightly bound dimers through atom-dimer and dimer-dimer collisions. In these collisions, a significant amount of energy is released. The reaction products leave the trap, leading to trap loss. We have constructed a simple set of rate equations describing these processes. Remarkably, even with only a few parameters, these equations reproduce the loss rate observed in all recent experiments, despite their widely different experimental conditions. Our studies show that the location of the maximum loss rate depends crucially on experimental parameters such as trap depth and temperature. These extrinsic characters show that this maximum is not a reliable probe of the nature of the underlying quantum states. The physics of our equations also explains some general trends found in current experiments. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1670772011-01-01T00:00:00Z
- Stability condition of a strongly interacting boson-fermion mixture across an interspecies Feshbach resonancehttp://hdl.handle.net/10722/167078Title: Stability condition of a strongly interacting boson-fermion mixture across an interspecies Feshbach resonance
Authors: Yu, ZQ; Zhang, S; Zhai, H
Abstract: We study the properties of dilute bosons immersed in a single-component Fermi sea across a broad boson-fermion Feshbach resonance. The stability of the mixture requires that the bare interaction between bosons exceeds a critical value, which is a universal function of the boson-fermion scattering length, and exhibits a maximum in the unitary region. We calculate the quantum depletion, momentum distribution, and the boson contact parameter across the resonance. The transition from condensate to molecular Fermi gas is also discussed. © 2011 American Physical Society.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1670782011-01-01T00:00:00Z
- BCS-BEC crossover induced by a synthetic non-Abelian gauge fieldhttp://hdl.handle.net/10722/167079Title: BCS-BEC crossover induced by a synthetic non-Abelian gauge field
Authors: Vyasanakere, JP; Zhang, S; Shenoy, VB
Abstract: We investigate the ground state of interacting spin-12 fermions in three dimensions at a finite density (ρ∼kF3) in the presence of a uniform non-Abelian gauge field. The gauge-field configuration (GFC) described by a vector λ?(λx,λy,λz) , whose magnitude λ determines the gauge coupling strength, generates a generalized Rashba spin-orbit interaction. For a weak attractive interaction in the singlet channel described by a small negative scattering length (k F|as|?1), the ground state in the absence of the gauge field (λ=0) is a BCS (Bardeen-Cooper-Schrieffer) superfluid with large overlapping pairs. With increasing gauge-coupling strength, a non-Abelian gauge field engenders a crossover of this BCS ground state to a BEC (Bose-Einstein condensate) of bosons even with a weak attractive interaction that fails to produce a two-body bound state in free vacuum (λ=0). For large gauge couplings (λ/kF?1), the BEC attained is a condensate of bosons whose properties are solely determined by the Rashba gauge field (and not by the scattering length so long as it is nonzero)-we call these bosons "rashbons." In the absence of interactions (as=0 -), the shape of the Fermi surface of the system undergoes a topological transition at a critical gauge coupling λT. For high-symmetry GFCs we show that the crossover from the BCS superfluid to the rashbon BEC occurs in the regime of λ near λT. In the context of cold atomic systems, these results make an interesting suggestion of obtaining BCS-BEC crossover through a route other than tuning the interaction between the fermions. © 2011 American Physical Society.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1670792011-01-01T00:00:00Z
- Anomalous conductance of a strongly interacting Fermi gas through a quantum point contacthttp://hdl.handle.net/10722/240952Title: Anomalous conductance of a strongly interacting Fermi gas through a quantum point contact
Authors: Liu, B; Zhai, H; Zhang, S
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2409522017-01-01T00:00:00Z
- Collective modes in a two-band superfluid of ultracold alkaline-earth-metal atoms close to an orbital Feshbach resonancehttp://hdl.handle.net/10722/240949Title: Collective modes in a two-band superfluid of ultracold alkaline-earth-metal atoms close to an orbital Feshbach resonance
Authors: Zhang, Y; Ding, S; Zhang, S
Abstract: We discuss the collective modes in an alkaline-earth-metal Fermi gas close to an orbital Feshbach resonance. Unlike the usual Feshbach resonance, the orbital Feshbach resonance in alkaline-earth-metal atoms realizes a two-band superfluid system where the fermionic nature of both the open and the closed channel has to be taken into account. We show that, apart from the usual Anderson-Bogoliubov mode which corresponds to the oscillation of total density, there also appears the long-sought Leggett mode corresponding to the oscillation of relative density between the two channels. The existence of the phonon and the Leggett modes and their evolution are discussed in detail. We show how these collective modes are reflected in the density response of the system.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2409492017-01-01T00:00:00Z
- Topological superfluids and the BEC-BCS crossover in the attractive Haldane-Hubbard modelhttp://hdl.handle.net/10722/240950Title: Topological superfluids and the BEC-BCS crossover in the attractive Haldane-Hubbard model
Authors: Zhang, Y; Xu, Z; Zhang, S
Abstract: Motivated by the recent realization of the Haldane model in a shaking optical lattice, we investigate the effects of attractive interaction and the BEC-BCS crossover in this model at and away from half-filling. We show that, contrary to the usual s-wave BEC-BCS crossover in the lattice, a topological superfluid with Chern number C=2 appears in an extended region of the phase space for intermediate strength of the attractive interaction on the interaction-density plane. When inversion symmetry is broken, a gapless weak topological state is realized. We also investigate the fluctuations in these superfluid phases and show that the Anderson-Bogoliubov mode is quadratic due to time-reversal symmetry breaking and the existence of an undamped Leggett mode in the strong-coupling limit. Near the topological phase transition, the damping of the Leggett mode reaches its maximum.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2409502017-01-01T00:00:00Z
- Effective theory and universal relations for Fermi gases near a <font size=-1><sub>d</sub></font>-wave-interaction resonancehttp://hdl.handle.net/10722/240947Title: Effective theory and universal relations for Fermi gases near a <font size=-1><sub>d</sub></font>-wave-interaction resonance
Authors: Zhang, PF; Zhang, S; Yu, ZH
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2409472017-01-01T00:00:00Z
- Normal-state properties of a resonantly interacting p-wave Fermi gashttp://hdl.handle.net/10722/253564Title: Normal-state properties of a resonantly interacting p-wave Fermi gas
Authors: Yao, J; Zhang, S
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10722/2535642018-01-01T00:00:00Z
- Three-dimensional Bose gas near a Feshbach resonancehttp://hdl.handle.net/10722/167082Title: Three-dimensional Bose gas near a Feshbach resonance
Authors: Borzov, D; Mashayekhi, MS; Zhang, S; Song, JL; Zhou, F
Abstract: In this paper, we explore the nature of three-dimensional Bose gases at large positive scattering lengths via resummation of dominating processes involving a minimum number of virtual atoms. We focus on the energetics of the nearly fermionized Bose gases beyond the usual dilute limit. We also find that an onset instability sets in at a critical scattering length, beyond which the near-resonance Bose gases become strongly coupled to molecules and lose the metastability. Near the point of instability, the chemical potential reaches a maximum, and the effect of the three-body forces can be estimated to be around a few percent. © 2012 American Physical Society.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/1670822012-01-01T00:00:00Z
- Evidence for correlated states in a cluster of bosons with Rashba spin-orbit couplinghttp://hdl.handle.net/10722/223880Title: Evidence for correlated states in a cluster of bosons with Rashba spin-orbit coupling
Authors: Xu, Z; Yu, Z; Zhang, S
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2238802016-01-01T00:00:00Z
- Spin-orbit Coupling in Optical Latticeshttp://hdl.handle.net/10722/215895Title: Spin-orbit Coupling in Optical Lattices
Authors: Zhang, S; Cole, WS; Paramekanti, A; Trivedi, N
Abstract: In this review,we discuss the physics of spin-orbit coupled quantumgases in optical lattices.After reviewing some relevant experimental techniques, we introduce the basic theoretical model and discuss some of its generic features. In particular,we concentrate on the interplay between spin-orbit coupling and strong interactions and show how it leads to various exotic quantum phases in both the Mott insulating and superfluid regimes. Phase transitions between the Mott and superfluid states are also discussed.
Read More: http://www.worldscientific.com/doi/abs/10.1142/9789814667746_0003
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2158952015-01-01T00:00:00Z
- Observation of the Leggett-Rice Effect in a Unitary Fermi Gashttp://hdl.handle.net/10722/208237Title: Observation of the Leggett-Rice Effect in a Unitary Fermi Gas
Authors: Trotzky, S; Beattie, S; Luciuk, C; Smale, S; Bardon, AB; Enss, T; Taylor, E; Zhang, S; Thywissen, JH
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2082372015-01-01T00:00:00Z
- Colliding clouds of strongly interacting spin-polarized fermionshttp://hdl.handle.net/10722/167081Title: Colliding clouds of strongly interacting spin-polarized fermions
Authors: Taylor, E; Zhang, S; Schneider, W; Randeria, M
Abstract: Motivated by a recent experiment at MIT, we consider the collision of two clouds of spin-polarized atomic Fermi gases close to a Feshbach resonance. We explain why two dilute gas clouds, with underlying attractive interactions between their constituents, bounce off each other in the strongly interacting regime. Our hydrodynamic analysis, in excellent agreement with experiment, gives strong evidence for a metastable many-body state with effective repulsive interactions. © 2011 American Physical Society.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1670812011-01-01T00:00:00Z
- Bose-Einstein condensates with spin-orbit interactionhttp://hdl.handle.net/10722/167080Title: Bose-Einstein condensates with spin-orbit interaction
Authors: Ho, TL; Zhang, S
Abstract: Motivated by recent experiments carried out by Spielman's group at NIST, we study a general scheme for generating families of gauge fields, spanning the scalar, spin-orbit, and non-Abelian regimes. The NIST experiments, which impart momentum to bosons while changing their spin state, can in principle realize all these. In the spin-orbit regime, we show that a Bose gas is a spinor condensate made up of two non-orthogonal dressed spin states carrying different momenta. As a result, its density shows a stripe structure with a contrast proportional to the overlap of the dressed states, which can be made very pronounced by adjusting the experimental parameters. © 2011 American Physical Society.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1670802011-01-01T00:00:00Z
- Theory of quantum oscillations in the vortex-liquid state of high-Tc superconductorshttp://hdl.handle.net/10722/183143Title: Theory of quantum oscillations in the vortex-liquid state of high-Tc superconductors
Authors: Banerjee, S; Zhang, S; Randeria, M
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/1831432013-01-01T00:00:00Z
- Universal Relations for a Fermi Gas Close to a p-Wave Interaction Resonancehttp://hdl.handle.net/10722/220608Title: Universal Relations for a Fermi Gas Close to a p-Wave Interaction Resonance
Authors: Yu, ZH; Thywissen, JH; Zhang, S
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2206082015-01-01T00:00:00Z
- Bose-Hubbard models with synthetic spin-orbit coupling: Mott insulators, spin textures, and superfluidityhttp://hdl.handle.net/10722/167083Title: Bose-Hubbard models with synthetic spin-orbit coupling: Mott insulators, spin textures, and superfluidity
Authors: Cole, WS; Zhang, S; Paramekanti, A; Trivedi, N
Abstract: Motivated by the experimental realization of synthetic spin-orbit coupling for ultracold atoms, we investigate the phase diagram of the Bose-Hubbard model in a non-Abelian gauge field in two dimensions. Using a strong coupling expansion in the combined presence of spin-orbit coupling and tunable interactions, we find a variety of interesting magnetic Hamiltonians in the Mott insulator (MI), which support magnetic textures such as spin spirals and vortex and Skyrmion crystals. An inhomogeneous mean-field treatment shows that the superfluid (SF) phases inherit these exotic magnetic orders from the MI and display, in addition, unusual modulated current patterns. We present a slave-boson theory which gives insight into such intertwined spin-charge orders in the SF, and discuss signatures of these orders in Bragg scattering, in situ microscopy, and dynamic quench experiments. © 2012 American Physical Society.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/1670832012-01-01T00:00:00Z
- Transverse Demagnetization Dynamics of a Unitary Fermi Gashttp://hdl.handle.net/10722/198071Title: Transverse Demagnetization Dynamics of a Unitary Fermi Gas
Authors: Bardon, AB; Beattie, S; Luciuk, C; Cairncross, W; Fine, D; Cheng, NS; Edge, GJA; Taylor, E; Zhang, S; Trotzky, S; Thywissen, JH
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/1980712014-01-01T00:00:00Z
- Fluctuation effects on the transport properties of unitary Fermi gaseshttp://hdl.handle.net/10722/207291Title: Fluctuation effects on the transport properties of unitary Fermi gases
Authors: Liu, BY; Zhai, H; Zhang, S
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/2072912014-01-01T00:00:00Z
- Superfluid density of a spin-orbit-coupled Bose gashttp://hdl.handle.net/10722/234774Title: Superfluid density of a spin-orbit-coupled Bose gas
Authors: Zhang, Y; Yu, Z; Ng, T; Zhang, S; Pitaevskii, L; Stringari, S
Abstract: We discuss the superfluid properties of a uniform, weakly interacting Bose-Einstein condensed gas with spin-orbit coupling, realized recently in experiments. We find a finite normal fluid density ρ n at zero temperature which turns out to be a function of the Raman coupling. In particular, the entire fluid becomes normal at the transition point from the zero momentum to the plane wave phase, even though the condensate fraction remains finite. We emphasize the crucial role played by the breaking of Galilean invariance and by the gapped branch of the elementary excitations whose contribution to various sum rules is discussed explicitly. Our predictions for the superfluid density are successfully compared with the available experimental results based on the measurement of the sound velocities.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2347742016-01-01T00:00:00Z
- Evolution of the Higgs mode in a fermion superfluid with tunable interactionshttp://hdl.handle.net/10722/225648Title: Evolution of the Higgs mode in a fermion superfluid with tunable interactions
Authors: Liu, B; Zhai, H; Zhang, S
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2256482016-01-01T00:00:00Z
- Realization and detection of Weyl semimetals and the chiral anomaly in cold atomic systemshttp://hdl.handle.net/10722/229397Title: Realization and detection of Weyl semimetals and the chiral anomaly in cold atomic systems
Authors: He, WY; Zhang, S; Law, KT
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2293972016-01-01T00:00:00Z
- Universal properties of Fermi gases in one dimensionhttp://hdl.handle.net/10722/237776Title: Universal properties of Fermi gases in one dimension
Authors: He, W; Chen, Y; Zhang, S; Guan, X
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2377762016-01-01T00:00:00Z
- Strongly interacting p-wave Fermi gas in two dimensions: Universal relations and breathing modehttp://hdl.handle.net/10722/239578Title: Strongly interacting p-wave Fermi gas in two dimensions: Universal relations and breathing mode
Authors: Zhang, Y; Zhang, S
Abstract: The contact is an important concept that characterizes the universal properties of a strongly interacting quantum gas. It appears in both thermodynamic (energy, pressure, etc.) and dynamic quantities (radio-frequency and Bragg spectroscopies, etc.) of the system. Very recently, the concept of contact was extended to higher partial waves; in particular, the p-wave contacts have been experimentally probed in recent experiments. So far, discussions on p-wave contacts have been limited to three dimensions. In this paper, we generalize the p-wave contacts to two dimensions and derive a series of universal relations, including the adiabatic relations, high-momentum distribution, virial theorem, and pressure relation. At the high-temperature and low-density limit, we calculate the p-wave contacts explicitly using virial expansion. A formula which directly connects the shift of the breathing-mode frequency and the p-wave contacts is given in a harmonically trapped system. Finally, we also derive the relationships between interaction parameters in three- and two-dimensional Fermi gases and discuss possible experimental realization of a two-dimensional Fermi gas with p-wave interactions.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2395782017-01-01T00:00:00Z
- Superfluidity of spin-orbit coupled (SOC) Bose-Einstein Condensate (BEC) http://hdl.handle.net/10722/238389Title: Superfluidity of spin-orbit coupled (SOC) Bose-Einstein Condensate (BEC)
Authors: Zhang, Y; Yu, Z; Ng, T; Zhang, S; Pitaevskii, L; Stringari, S
Abstract: We discuss the superfluid properties of a Bose-Einstein condensed gas with spin-orbit coupling, recently realized in experiments. We find a finite normal fluid density ρ_n at zero temperature which turns out to be a function of the Raman coupling. In particular, the entire fluid becomes normal at the transition point from the zero momentum to the plane wave phase, even though the condensate fraction remains finite. We emphasize the crucial role played by the gapped branch of the elementary excitations and discuss its contributions to various sum rules. Finally, we prove that an independent definition of superfluid density , using the phase twist method, satisfies the identity ρ_n + ρ_s = ρ, the total density, despite the breaking of Galilean invariance.
Description: Session 2.2 Condensed Matter Physics
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2383892016-01-01T00:00:00Z
- P-wave contacts for two dimensional quatum gashttp://hdl.handle.net/10722/238393Title: P-wave contacts for two dimensional quatum gas
Authors: Zhang, Y; Yu, Z; Zhang, S
Abstract: The s-wave contact has played an important role in our understanding of the strongly interacting Fermi gases. Recently, theoretical and experimental work has shown that two similar contacts exist for a p-wave interacting Fermi gas in three-dimensions. In this work, we extend the considerations to two dimensional spineless Fermi gas and derive exact results regarding the energy, momentum distributions and in par- ticular, shifts of monopole frequency in a harmonic trap. Asymptotic formula for the frequency shift is given at high temperature via virial expansion and this can be checked by future experiments.
Description: Session S50: Strongly Interacting Bose and Fermi Gases: Abstract: S50.00001: http://meetings.aps.org/link/BAPS.2016.MAR.S50.1
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2383932016-01-01T00:00:00Z
- Momentum distribution and contacts of one-dimensional spinless Fermi gases with an attractive p-wave interactionhttp://hdl.handle.net/10722/259435Title: Momentum distribution and contacts of one-dimensional spinless Fermi gases with an attractive p-wave interaction
Authors: Yin, X; Guan, XW; Zhang, YB; Su, HB; Zhang, S
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10722/2594352018-01-01T00:00:00Z
- The BEC-BCS Crossover: Some History and Some General Observationshttp://hdl.handle.net/10722/190888Title: The BEC-BCS Crossover: Some History and Some General Observations
Authors: Leggett, AJ; Zhang, S
Abstract: While the experimental realization in ultracold Fermi alkali gases of the phenomenon we now call the “BEC–BCS crossover” was attained only in the last few years, theoretical considerations of this issue go back a lot further, and refer to other systems as well. In the first part of this chapter we review some of this history, while in the second half we make some general comments on the current theoretical situation with respect to the specific ultracold-gas implementation.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/1908882012-01-01T00:00:00Z
- Theoretical investigation of a single molecule device: Geometrical configurations and electronic propertieshttp://hdl.handle.net/10722/206540Title: Theoretical investigation of a single molecule device: Geometrical configurations and electronic properties
Authors: Yuan, Z; Su, CR; Zhang, S; Li, JM
Abstract: Using the first-principle molecular dynamics simulations, we have studied the molecular geometrical configurations as well as the corresponding electronic structures of a single molecule device assembled by the mechanically controllable break junction technique with variations of the electrode distance. There are some very interesting features varying with the electrode distance.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/2065402004-01-01T00:00:00Z
- Relativistic multichannel theory: Theoretical study of C+ autoionization stateshttp://hdl.handle.net/10722/206539Title: Relativistic multichannel theory: Theoretical study of C+ autoionization states
Authors: Xia, D; Zhang, S; Peng, YL; Li, JM
Abstract: Based on relativistic multichannel theory, the autoionization states of C+ are studied. We calculate all the autoionization states in the energy region of 193900 ∼ 231700 cm-1, and the results are in good agreement with the experimental data. The energy structure we obtain will be important in the dielectronic recombination processes, which plays a key role in determining the abundance of carbon in a nebula.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10722/2065392003-01-01T00:00:00Z
- Production of Feshbach molecules induced by spin-orbit coupling in Fermi gaseshttp://hdl.handle.net/10722/197631Title: Production of Feshbach molecules induced by spin-orbit coupling in Fermi gases
Authors: Fu, ZK; Huang, LH; Meng, ZM; Wang, PJ; Zhang, L; Zhang, S; Zhai, H; Zhang, P; Zhang, J
Abstract: The search for topological superconductors is a challenging task1,2. One of the most promising directions is to use spinorbit coupling through which an s-wave superconductor can induce unconventional p-wave pairing in a spin-polarized metal3,4. Recently, synthetic spin-orbit couplings have been realized in cold-atom systems5-16 where instead of a proximity effect, s-wave pairing originates from a resonant coupling between s-wave molecules and itinerant atoms17. Here we demonstrate a dynamic process in which spin-orbit coupling coherently produces s-wave Feshbach molecules from a fully polarized Fermi gas, and induces a coherent oscillation between these two. This demonstrates experimentally that spin-orbit coupling does coherently couple singlet and triplet states, and implies that the bound pairs of this system have a triplet p-wave component, which can become a topological superfluid by further cooling to condensation and confinement to one dimension.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/1976312014-01-01T00:00:00Z
- Quantum Spin Dynamics in a Normal Bose Gas with Spin-Orbit Couplinghttp://hdl.handle.net/10722/263258Title: Quantum Spin Dynamics in a Normal Bose Gas with Spin-Orbit Coupling
Authors: TANG, WH; Zhang, S
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10722/2632582018-01-01T00:00:00Z
- 量子气体中的输运行为http://hdl.handle.net/10722/269443Title: 量子气体中的输运行为; Transport phenomena in dilute quantum gases
Authors: Zhang, S
Abstract: 输运测量是了解物质性质的一个重要手段.本文简单介绍最近在量子气体中实现的输运实验及其主要结论，包括在类似于介观物理器件中的Landauer输运和强相互作用费米气体中的自旋输运行为.我们着重讨论自旋动力学的特殊性以及其由于全同粒子相互作用所导致的特殊自旋扩散流的形式.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10722/2694432019-01-01T00:00:00Z
- Fermi-Liquid Description of a Single-Component Fermi Gas with p-Wave Interactionshttp://hdl.handle.net/10722/275142Title: Fermi-Liquid Description of a Single-Component Fermi Gas with p-Wave Interactions
Authors: Ding, S; Zhang, S
Abstract: We study the Fermi liquid properties of a single component Fermi gas with p-wave interactions. In the weak repulsive limit, we obtain exact perturbative expansions for the ground state energy, the chemical potential, and the effective mass of the Landau quasiparticle up to second order in scattering volume
a. We also calculated the corresponding Landau functions and Landau parameters and show that they satisfy the general Fermi liquid identities. Using the Landau transport equation, we show that undamped zero sound only appears in the second order in scattering volume, in contrast to the s-wave case.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10722/2751422019-01-01T00:00:00Z
- Dynamic Kosterlitz-Thouless theory for two-dimensional ultracold atomic gaseshttp://hdl.handle.net/10722/293412Title: Dynamic Kosterlitz-Thouless theory for two-dimensional ultracold atomic gases
Authors: Wu, Z; Zhang, S; Zhai, H
Abstract: In this paper we develop a theory for the first and second sounds in a two-dimensional atomic gas across the superfluid transition based on the dynamic Koterlitz-Thouless theory. We employ a set of modified two-fluid hydrodynamic equations which incorporate the dynamics of the quantized vortices, rather than the conventional ones for a three-dimensional superfluid. As far as the sound dispersion equation is concerned, the modification is essentially equivalent to replacing the static superfluid density with a frequency-dependent one, renormalized by the frequency-dependent “dielectric constant” of the vortices. This theory has two direct consequences. First, because the renormalized superfluid density at finite frequencies does not display discontinuity across the superfluid transition, in contrast to the static superfluid density, the sound velocities vary smoothly across the transition. Second, the theory includes dissipation due to free vortices and thus naturally describes the sound-to-diffusion crossover for the second sound in the normal phase. With only one fitting parameter, our theory gives a perfect agreement with the experimental measurements of sound velocities across the transition, as well as the quality factor in the vicinity of the transition. The predictions from this theory can be further verified by future experiments.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10722/2934122020-01-01T00:00:00Z
- Role of Effective Range in the Bulk Viscosity of Resonantly Interacting s- and p-Wave Fermi Gaseshttp://hdl.handle.net/10722/295483Title: Role of Effective Range in the Bulk Viscosity of Resonantly Interacting s- and p-Wave Fermi Gases
Authors: Maki, J; Zhang, S
Abstract: We investigate the role of the effective range on the bulk viscosity of s- and p-wave Fermi gases. At resonance, the presence of the effective range breaks the scale invariance of the system, and hence results in a nonzero bulk viscosity. However, we show that the effective range plays a very different role in the two cases. In the s-wave case, the role of the effective range is perturbative, and its contribution to the bulk viscosity vanishes in the limit of zero effective range. On the other hand, the effective range in p-wave Fermi gases leads to a nonzero bulk viscosity, even in the zero-range limit. We employ a general diagrammatic approach to compute the bulk viscosity spectral function that includes the effects of the effective range. We then compute the analytic expressions for the spectral function in the high temperature limit, at low and high frequencies. We also derive the sum rules for the bulk viscosity spectral function for both s- and p-wave gases.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10722/2954832020-01-01T00:00:00Z
- Manipulation of heteronuclear spin dynamics with microwave and vector light shifthttp://hdl.handle.net/10722/286297Title: Manipulation of heteronuclear spin dynamics with microwave and vector light shift
Authors: Li, L; Zhu, B; Lu, B; Zhang, S; Wang, D
Abstract: We report the observation and manipulation of heteronuclear spin dynamics in a spin-1 mixture of ultracold Rb87 and Na23 atoms. The dynamics is driven by the interspecies spin-dependent interaction and shows a pronounced dependence on magnetic fields with influences from both linear and quadratic Zeeman shifts. Similar to the well-studied homonuclear cases, the interspecies spin dynamics can be controlled by tuning the quadratic Zeeman shift with far-detuned microwave fields. In addition, we successfully realize spin dynamics' control with vector light shifts which act as a species-selective effective magnetic field on Rb87 atoms. Both methods show negligible loss of atoms thus will be powerful techniques for investigating spin dynamics with fast temporal and high spatial resolutions.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10722/2862972020-01-01T00:00:00Z
- Collective excitations in two-dimensional SU(N) Fermi gases with tunable spinhttp://hdl.handle.net/10722/287365Title: Collective excitations in two-dimensional SU(N) Fermi gases with tunable spin
Authors: He, CD; Ren, Z; Song, B; Zhao, E; Lee, J; Zhang, YC; Zhang, S; Jo, GB
Abstract: We measure collective excitations of a harmonically trapped two-dimensional (2D) SU(N) Fermi gas of
173Yb confined to a stack of layers formed by a one-dimensional optical lattice. Quadrupole and breathing modes are excited and monitored in the collisionless regime | ln(kFa2D)|≫1 with tunable spin. We observe that the quadrupole mode frequency decreases with increasing number of spin components due to the amplification of the interaction effect by N in agreement with a theoretical prediction based on 2D kinetic equations. The breathing mode frequency, however, is measured to be twice the dipole oscillation frequency regardless of N. We also follow the evolution of collective excitations in the dimensional crossover from two to three dimensions and characterize the damping rate of quadrupole and breathing modes for tunable SU(N) fermions, both of which reveal the enhanced interparticle collisions for larger spin. Our result paves the way to investigate the collective property of 2D SU(N) Fermi liquid with enlarged spin.
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10722/2873652020-01-01T00:00:00Z
- Grüneisen parameters: Origin, identity, and quantum refrigerationhttp://hdl.handle.net/10722/295743Title: Grüneisen parameters: Origin, identity, and quantum refrigeration
Authors: Yu, Y; Zhang, S; Guan, XW
Abstract: In solid-state physics, the Gruneisen parameter (GP) was first introduced to study the effect of volume change of a crystal lattice on its vibrational frequencies and has since been widely used to investigate the characteristic energy scales of systems associated with the changes of external potentials. However, the GP is less investigated in gas systems and especially strongly interacting quantum gases. Here we report on some general results on the origin of the GP, an identity, and caloric effects in ultracold quantum gases. We prove that there exists a simple identity among three different types of GPs, quantifying the caloric effect induced by variations of volume, magnetic field, and interaction, respectively. Using exact Bethe ansatz solutions, we present a rigorous study of these different GPs and the quantum refrigeration in one-dimensional Bose and Fermi gases. Based on the exact equations of states of these systems, we further obtain analytic results for singular behavior of the GPs and the caloric effects at quantum criticality. We also predict the existence of the lowest temperature for cooling near a quantum phase transition. It turns out that the interaction ramp up and down in quantum gases provide a promising protocol of quantum refrigeration in addition to the usual adiabatic demagnetization cooling in solid-state materials.
Description: Hybrid open access
Wed, 01 Jan 2020 00:00:00 GMThttp://hdl.handle.net/10722/2957432020-01-01T00:00:00Z
- Dynamics of Strongly Interacting Fermi Gases with Time-Dependent Interactions: Consequence of Conformal Symmetryhttp://hdl.handle.net/10722/310936Title: Dynamics of Strongly Interacting Fermi Gases with Time-Dependent Interactions: Consequence of Conformal Symmetry
Authors: Maki, JA; Zhang, S; Zhou, F
Sat, 01 Jan 2022 00:00:00 GMThttp://hdl.handle.net/10722/3109362022-01-01T00:00:00Z