We investigate domain wall excitations in a two-component Bose–Einstein condensate with two-body interactions and pair-transition effects. It is shown that domain wall excitations can be described exactly by kink and...We investigate domain wall excitations in a two-component Bose–Einstein condensate with two-body interactions and pair-transition effects. It is shown that domain wall excitations can be described exactly by kink and anti-kink excitations in each component. The domain wall solutions are given analytically, which exist with different conditions compared with the domain wall reported before. Bubble-droplet structure can be also obtained from the fundamental domain wall, and their interactions are investigated analytically. Especially, domain wall interactions demonstrate some striking particle transition dynamics. These striking transition effects make the domain wall admit quite different collision behavior, in contrast to the collision between solitons or other nonlinear waves. The collisions between kinks induce some phase shift, which makes the domain wall change greatly. Their collisions can be elastic or inelastic with proper combination of fundamental domain walls. These characters can be used to manipulate one domain wall by interacting with other ones.展开更多
We theoretically study the transition dynamics of a two-component Bose-Einstein condensate driven by a train of weak δ-shaped laser pulses. We find that the atomic system can experience peculiar resonant transition e...We theoretically study the transition dynamics of a two-component Bose-Einstein condensate driven by a train of weak δ-shaped laser pulses. We find that the atomic system can experience peculiar resonant transition even under weak optical excitations and derive the resonance condition by the perturbation method. Employing this mechanism, we propose a scheme to obtain an atomic ensemble with desired odd/even atom number and also a scheme to prepare a nonclassical state of the many-body system with fixed atom number.展开更多
We report the analytical nonantonomous soliton solutions (NSSs) for two-component Bose-Einstein condensates with the presence of a time-dependent potential. These solutions show that the time-dependent potential can...We report the analytical nonantonomous soliton solutions (NSSs) for two-component Bose-Einstein condensates with the presence of a time-dependent potential. These solutions show that the time-dependent potential can affect the velocity of NSS. The velocity shows the characteristic of both increasing and oscillation with time. A detailed analysis for the asymptotic behavior of NSSs demonstrates that the collision of two NSSs of each component is elastic.展开更多
The ground states of two-component miscible Bose–Einstein condensates(BECs) confined in a rotating annular trap are obtained by using the Thomas–Fermi(TF) approximation method.The ground state density distributi...The ground states of two-component miscible Bose–Einstein condensates(BECs) confined in a rotating annular trap are obtained by using the Thomas–Fermi(TF) approximation method.The ground state density distribution of the condensates experiences a transition from a disc shape to an annulus shape either when the angular frequency increases and the width and the center height of the trap are fixed,or when the width and the center height of the trap increase and the angular frequency is fixed.Meantime the numerical solutions of the ground states of the trapped two-component miscible BECs with the same condition are obtained by using imaginary-time propagation method.They are in good agreement with the solutions obtained by the TF approximation method.The ground states of the trapped two-component immiscible BECs are also given by using the imaginary-time propagation method.Furthermore,by introducing a normalized complex-valued spinor,three kinds of pseudospin textures of the BECs,i.e.,giant skyrmion,coaxial double-annulus skyrmion,and coaxial three-annulus skyrmion,are found.展开更多
We investigate a kind of solitons in the two-component Bose-Einstein condensates with axisymmetric configurations in the R2 × S1 space. The corresponding topological structure is referred to as Hopfion. The spin ...We investigate a kind of solitons in the two-component Bose-Einstein condensates with axisymmetric configurations in the R2 × S1 space. The corresponding topological structure is referred to as Hopfion. The spin texture differs from the conventional three-dimensional (3D) skyrmion and knot, which is characterized by two homotopy invariants. The stability of the Hopfion is verified numerically by evolving the Gross-Pitaevskii equations in imaginary time.展开更多
The dynamics of spin–orbit-coupled Bose–Einstein condensate with parity-time symmetry through a moving obstacle potential is simulated numerically. In the miscible two-component condensate, the formation of the K...The dynamics of spin–orbit-coupled Bose–Einstein condensate with parity-time symmetry through a moving obstacle potential is simulated numerically. In the miscible two-component condensate, the formation of the Kármán vortex street is observed in one component, while ‘the half-quantum vortex street' is observed in the other component. Other patterns of vortex shedding, such as oblique vortex dipoles, V-shaped vortex pairs, irregular turbulence, and combined modes of various wakes, can also be found. The ratio of inter-vortex spacing in one row to the distance between vortex rows is approximately0.18, which is less than the stability condition 0.28 of classical fluid. The drag force acting on the obstacle potential is simulated. The parametric regions of Kármán vortex street and other vortex patterns are calculated. The range of Kármán vortex street is surrounded by the region of combined modes. In addition, spin–orbit coupling disrupts the symmetry of the system and the gain-loss affects the local particle distribution of the system, which leads to the local symmetry breaking of the system, and finally influences the stability of the Kármán vortex street. Finally, we propose an experimental protocol to realize the Kármán vortex street in a system.展开更多
We present several families of exact solutions to a system of coupled nonlinear Schrodinger equations. The model describes a binary mixture of two Bose-Einstein condensates in a magnetic trap potential. Using a mappin...We present several families of exact solutions to a system of coupled nonlinear Schrodinger equations. The model describes a binary mixture of two Bose-Einstein condensates in a magnetic trap potential. Using a mapping deformation method, we find exact periodic wave and soliton solutions, including bright and dark soliton pairs.展开更多
With the method of Green's function, we investigate the energy spectra of two-component ultracold bosonic atoms in optical lattices. We find that there are two energy bands for each component. The critical conditi...With the method of Green's function, we investigate the energy spectra of two-component ultracold bosonic atoms in optical lattices. We find that there are two energy bands for each component. The critical condition of the superfluid-Mott insulator phase transition is determined by the energy band structure. We also find that the nearest neighboring and on-site interactions fail to change the structure of energy bands, but shift the energy bands only.According to the conditions of the phase transitions, three stable superfluid and Mott insulating phases can be found by adjusting the experiment parameters. We also discuss the possibility of observing these new phases and their transitions in further experiments.展开更多
We consider two coupled Gross Pitaevskii equations describing a two-component Bose Einstein condensate with time-dependent atomic interactions loaded in an external harmonic potential, and investigate the dynamics of ...We consider two coupled Gross Pitaevskii equations describing a two-component Bose Einstein condensate with time-dependent atomic interactions loaded in an external harmonic potential, and investigate the dynamics of vector solitons. By using a direct method, we construct a novel family of vector soliton solutions, which are the linear combination between dark and bright solitons in each component. Our results show that due to the superposition between dark and bright solitons, such vector solitons possess many novel and interesting properties. The dynamics of vector solitons can be controlled by the Feshbach resonance technique, and the vector solitons can keep the dynamic stability against the variation of the scattering length.展开更多
We investigate phase diffusion of a two-component Bose--Einstein condensates prepared initially in arbitrary coherent spin state |θ0,φ0|. Analytical expression of the phase-diffusion time is presented for θ0~π/...We investigate phase diffusion of a two-component Bose--Einstein condensates prepared initially in arbitrary coherent spin state |θ0,φ0|. Analytical expression of the phase-diffusion time is presented for θ0~π/2 case. In comparison with the symmetrical case (i.e., θ0=π/2), we find that the diffusion process becomes slow due to the reduced atom number variance.展开更多
We investigate modulational instability(MI) of a coupled two-component Bose–Einstein condensates in a rotating ring trap. The excitation spectrum and the MI condition of the system are presented analytically. We find...We investigate modulational instability(MI) of a coupled two-component Bose–Einstein condensates in a rotating ring trap. The excitation spectrum and the MI condition of the system are presented analytically. We find that the coupling between the two components strongly modifies the MI condition, and the MI condition is phase-dependent.Furthermore, we discuss the effect of MI on both density excitation and spin excitation. If the inter- and intra-component interaction strengths are all equal, the MI causes density excitation but not spin excitation, and if the inter- and intracomponent interaction strengths are different, the MI causes both density excitation and spin excitation. Our results provide a promising approach for controlling the stability and excitation of a rotating two-component Bose–Einstein condensates by modulating its coupling strength and interaction strength.展开更多
This paper investigates the dynamical properties of nonstationary solutions in one-dimensional two-component Bose-Einstein condensates. It gives three kinds of stationary solutions to this model and develops a general...This paper investigates the dynamical properties of nonstationary solutions in one-dimensional two-component Bose-Einstein condensates. It gives three kinds of stationary solutions to this model and develops a general method of constructing nonstationary solutions. It obtains the unique features about general evolution and soliton evolution of nonstationary solutions in this model.展开更多
We present two kinds of exact vector-soliton solutions for coupled nonlinear Schrodinger equations with time- varying interactions and time-varying harmonic potential. Using the variational approach, we investigate th...We present two kinds of exact vector-soliton solutions for coupled nonlinear Schrodinger equations with time- varying interactions and time-varying harmonic potential. Using the variational approach, we investigate the dynamics of the vector solitons. It is found that the two bright sol/tons oscillate about slightly and pass through each other around the equilibration state which means that they are stable under our modeh At the same time, we obtain the opposite situation for dark-dark solitons.展开更多
We investigate the exact nonstationary solutions of a two-component Bose-Einstein condensate whichcompose of two species having different atomic masses. We also consider the interesting behavior of the atomic velocity...We investigate the exact nonstationary solutions of a two-component Bose-Einstein condensate whichcompose of two species having different atomic masses. We also consider the interesting behavior of the atomic velocityand the flow density. It is shown that the motion of the two components can be controlled by the experimental parameters.展开更多
The interference of the two-component Bose-Einstein condensates with a coupling drive in the presence of the dissipation is studied. We find that when the two-component Bose-Einstein condensates are initially in the c...The interference of the two-component Bose-Einstein condensates with a coupling drive in the presence of the dissipation is studied. We find that when the two-component Bose-Einstein condensates are initially in the coherent states, for the smaller dissipation parameters compared with that of the rf frequency ωrf, the interference intensity exhibits damply oscillation behavior, whereas when the dissipation parameters are larger than that of the ωrf, the interference intensity exhibits a fast attenuation behavior. As a comparison, the interference intensity in the absence of the dissipation is also studied. We conclude that the dissipation of the system can be evaluated by selecting the ωrf experimentally.展开更多
We investigate the Landau-Zener tunnelling of two-component Rose-Einstein condensates (BECs) in opticallattices.In the neighborhood of the Rrillouin zone edge,the system can be reduced to two coupled nonlinear two-lev...We investigate the Landau-Zener tunnelling of two-component Rose-Einstein condensates (BECs) in opticallattices.In the neighborhood of the Rrillouin zone edge,the system can be reduced to two coupled nonlinear two-levelmodels.From the models,we calculate the change of the tunnelling probability for each component with the linearsweeping rate.It is found that the probability for each component exhibits regular oscillating behavior for the largersweeping rate,but for smaller rate the oscillation is irregular.Moreover,the asymmetry of the tunnelling between thetwo components can be induced by the unbalanced initial populations or the inequality of the two self-interactions whenthe cross-interaction between the components exists.The result can not be found in the single component BECs.展开更多
We present three families of exact matter-wave soliton solutions for an effective one-dimension twocomponent Bose-Einstein condensates(BECs) with tunable interactions,harmonic potential and gain or loss term. We inves...We present three families of exact matter-wave soliton solutions for an effective one-dimension twocomponent Bose-Einstein condensates(BECs) with tunable interactions,harmonic potential and gain or loss term. We investigate the dynamics of bright-bright solitons,bright-dark solitons and dark-dark solitons for the time-dependent expulsive harmonic trap potential,periodically modulated harmonic trap potential,and kinklike modulated harmonic trap potential.Through the Feshbach resonance,these dynamics can be realized in experiments by suitable control of time-dependent trap parameters,atomic interactions,and interaction with thermal cloud.展开更多
The elementary excitation spectrum of a two-component Bose-Einstein condensate in different hyperfine states is obtained by Green's function method. It is found to have two branches. In the long wave-length limit, th...The elementary excitation spectrum of a two-component Bose-Einstein condensate in different hyperfine states is obtained by Green's function method. It is found to have two branches. In the long wave-length limit, the two branches of the excitation spectrum are reduced to one phonon excitation and one single-particle excitation. The single-particle one has an energy gap. When the energy gap exists, we study the Landau critical velocity and the depletion of the condensate. With the obtained Green's functions, we calculate the structure factor of a two-component condensate. It is found that the static structure factor comprises only the branch of the phonon excitation and the single-particle excitation makes no contribution to the structure factor.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.11775176)the Major Basic Research Program of the Natural Science Foundation of Shaanxi Province,China(Grant No.2018KJXX-094)the Key Innovative Research Team of Quantum Many-Body Theory and Quantum Control in Shaanxi Province,China(Grant No.2017KCT-12)
文摘We investigate domain wall excitations in a two-component Bose–Einstein condensate with two-body interactions and pair-transition effects. It is shown that domain wall excitations can be described exactly by kink and anti-kink excitations in each component. The domain wall solutions are given analytically, which exist with different conditions compared with the domain wall reported before. Bubble-droplet structure can be also obtained from the fundamental domain wall, and their interactions are investigated analytically. Especially, domain wall interactions demonstrate some striking particle transition dynamics. These striking transition effects make the domain wall admit quite different collision behavior, in contrast to the collision between solitons or other nonlinear waves. The collisions between kinks induce some phase shift, which makes the domain wall change greatly. Their collisions can be elastic or inelastic with proper combination of fundamental domain walls. These characters can be used to manipulate one domain wall by interacting with other ones.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFA0301504)the National Natural Science Foundation of China(Grant Nos.61835013 and 11774362)
文摘We theoretically study the transition dynamics of a two-component Bose-Einstein condensate driven by a train of weak δ-shaped laser pulses. We find that the atomic system can experience peculiar resonant transition even under weak optical excitations and derive the resonance condition by the perturbation method. Employing this mechanism, we propose a scheme to obtain an atomic ensemble with desired odd/even atom number and also a scheme to prepare a nonclassical state of the many-body system with fixed atom number.
基金supported by the Key Project of the Chinese Ministry of Education(Grant No.2011015)the Natural Science Foundation of Hebei Province of China(Grant No.A2012202023)
文摘We report the analytical nonantonomous soliton solutions (NSSs) for two-component Bose-Einstein condensates with the presence of a time-dependent potential. These solutions show that the time-dependent potential can affect the velocity of NSS. The velocity shows the characteristic of both increasing and oscillation with time. A detailed analysis for the asymptotic behavior of NSSs demonstrates that the collision of two NSSs of each component is elastic.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.91430109 and 11404198)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20111401110004)the Natural Science Foundation of Shanxi Province,China(Grant No.2014011005-3)
文摘The ground states of two-component miscible Bose–Einstein condensates(BECs) confined in a rotating annular trap are obtained by using the Thomas–Fermi(TF) approximation method.The ground state density distribution of the condensates experiences a transition from a disc shape to an annulus shape either when the angular frequency increases and the width and the center height of the trap are fixed,or when the width and the center height of the trap increase and the angular frequency is fixed.Meantime the numerical solutions of the ground states of the trapped two-component miscible BECs with the same condition are obtained by using imaginary-time propagation method.They are in good agreement with the solutions obtained by the TF approximation method.The ground states of the trapped two-component immiscible BECs are also given by using the imaginary-time propagation method.Furthermore,by introducing a normalized complex-valued spinor,three kinds of pseudospin textures of the BECs,i.e.,giant skyrmion,coaxial double-annulus skyrmion,and coaxial three-annulus skyrmion,are found.
基金supported by the National Natural Science Foundation of China(Grant No.11374036)the National Basic Research Program of China(Grant No.2012CB821403)
文摘We investigate a kind of solitons in the two-component Bose-Einstein condensates with axisymmetric configurations in the R2 × S1 space. The corresponding topological structure is referred to as Hopfion. The spin texture differs from the conventional three-dimensional (3D) skyrmion and knot, which is characterized by two homotopy invariants. The stability of the Hopfion is verified numerically by evolving the Gross-Pitaevskii equations in imaginary time.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12065022 and 12147213)。
文摘The dynamics of spin–orbit-coupled Bose–Einstein condensate with parity-time symmetry through a moving obstacle potential is simulated numerically. In the miscible two-component condensate, the formation of the Kármán vortex street is observed in one component, while ‘the half-quantum vortex street' is observed in the other component. Other patterns of vortex shedding, such as oblique vortex dipoles, V-shaped vortex pairs, irregular turbulence, and combined modes of various wakes, can also be found. The ratio of inter-vortex spacing in one row to the distance between vortex rows is approximately0.18, which is less than the stability condition 0.28 of classical fluid. The drag force acting on the obstacle potential is simulated. The parametric regions of Kármán vortex street and other vortex patterns are calculated. The range of Kármán vortex street is surrounded by the region of combined modes. In addition, spin–orbit coupling disrupts the symmetry of the system and the gain-loss affects the local particle distribution of the system, which leads to the local symmetry breaking of the system, and finally influences the stability of the Kármán vortex street. Finally, we propose an experimental protocol to realize the Kármán vortex street in a system.
基金Project supported by the National Natural Science Foundation of China(Grant Nos 10575087 and 10302018), and the Natural Science Foundation of Zhejiang Province, China (Grant No Y605056).
文摘We present several families of exact solutions to a system of coupled nonlinear Schrodinger equations. The model describes a binary mixture of two Bose-Einstein condensates in a magnetic trap potential. Using a mapping deformation method, we find exact periodic wave and soliton solutions, including bright and dark soliton pairs.
文摘With the method of Green's function, we investigate the energy spectra of two-component ultracold bosonic atoms in optical lattices. We find that there are two energy bands for each component. The critical condition of the superfluid-Mott insulator phase transition is determined by the energy band structure. We also find that the nearest neighboring and on-site interactions fail to change the structure of energy bands, but shift the energy bands only.According to the conditions of the phase transitions, three stable superfluid and Mott insulating phases can be found by adjusting the experiment parameters. We also discuss the possibility of observing these new phases and their transitions in further experiments.
基金Project supported by the National Key Basic Research Program of China (Grant Nos. 2011CB921502,2012CB821305,2009CB930701,and 2010CB922904)the National Natural Science Foundation of China (NSFC) (Grant Nos. 10934010 and60978019)+1 种基金the NSFC-RGC (Grant Nos. 11061160490 and 1386-N-HKU748/10)the Key Program of the Chinese Ministry of Education (Grant No. 2011015)
文摘We consider two coupled Gross Pitaevskii equations describing a two-component Bose Einstein condensate with time-dependent atomic interactions loaded in an external harmonic potential, and investigate the dynamics of vector solitons. By using a direct method, we construct a novel family of vector soliton solutions, which are the linear combination between dark and bright solitons in each component. Our results show that due to the superposition between dark and bright solitons, such vector solitons possess many novel and interesting properties. The dynamics of vector solitons can be controlled by the Feshbach resonance technique, and the vector solitons can keep the dynamic stability against the variation of the scattering length.
基金supported by the National Natural Science Foundation of China (Grant No. 10804007)the Special Research Foundation and Development Program (Grant No. 200800041003)Research Funds of Beijing Jiaotong University (Grant No. 2007XM049)
文摘We investigate phase diffusion of a two-component Bose--Einstein condensates prepared initially in arbitrary coherent spin state |θ0,φ0|. Analytical expression of the phase-diffusion time is presented for θ0~π/2 case. In comparison with the symmetrical case (i.e., θ0=π/2), we find that the diffusion process becomes slow due to the reduced atom number variance.
基金Supported by the National Natural Science Foundation of China under Grant No.11465008the Hunan Provincial Natural Science Foundation under Grant No.2015JJ2114+2 种基金the Scientific Research Fund of Hunan Provincial Education Department under Grant Nos.14A118,13C881Science and Technology Innovative Research Team in Higher Educational Instituions of Hunan ProvinceScience Research Foundation of Xiangnan University under Grant No.2012–126(41)
文摘We investigate modulational instability(MI) of a coupled two-component Bose–Einstein condensates in a rotating ring trap. The excitation spectrum and the MI condition of the system are presented analytically. We find that the coupling between the two components strongly modifies the MI condition, and the MI condition is phase-dependent.Furthermore, we discuss the effect of MI on both density excitation and spin excitation. If the inter- and intra-component interaction strengths are all equal, the MI causes density excitation but not spin excitation, and if the inter- and intracomponent interaction strengths are different, the MI causes both density excitation and spin excitation. Our results provide a promising approach for controlling the stability and excitation of a rotating two-component Bose–Einstein condensates by modulating its coupling strength and interaction strength.
基金supported by the National Natural Science Foundation of China (Grant No. 1057411)the Foundation for Researching Group by Beijing Normal Universitythe Foundation for Outstanding Doctoral Dissertation by Beijing Normal University
文摘This paper investigates the dynamical properties of nonstationary solutions in one-dimensional two-component Bose-Einstein condensates. It gives three kinds of stationary solutions to this model and develops a general method of constructing nonstationary solutions. It obtains the unique features about general evolution and soliton evolution of nonstationary solutions in this model.
基金Projects supported by the National Natural Science Foundation of China (Grant Nos. 10775049 and 10375022)
文摘We present two kinds of exact vector-soliton solutions for coupled nonlinear Schrodinger equations with time- varying interactions and time-varying harmonic potential. Using the variational approach, we investigate the dynamics of the vector solitons. It is found that the two bright sol/tons oscillate about slightly and pass through each other around the equilibration state which means that they are stable under our modeh At the same time, we obtain the opposite situation for dark-dark solitons.
基金The project supported by National Natural Science Foundation of China under Grant No. 10574060 and Natural Science Foundation of Beijing under Grant No. 1072010
文摘由使用不变的理论,我们在在每冷凝物的 interatomicinteraction 的力量等于的案例下面与 a coupling 开车学习 two-componentBose-Einstein 冷凝物的阶段内部种类相互作用。动态、几何的阶段分别地被介绍。Aharonov—Anandan 阶段也在轮转的进化下面被获得。
基金Supported by National Natural Science Foundation of China under Grant Nos. 10775049 and 10375022
文摘We investigate the exact nonstationary solutions of a two-component Bose-Einstein condensate whichcompose of two species having different atomic masses. We also consider the interesting behavior of the atomic velocityand the flow density. It is shown that the motion of the two components can be controlled by the experimental parameters.
文摘The interference of the two-component Bose-Einstein condensates with a coupling drive in the presence of the dissipation is studied. We find that when the two-component Bose-Einstein condensates are initially in the coherent states, for the smaller dissipation parameters compared with that of the rf frequency ωrf, the interference intensity exhibits damply oscillation behavior, whereas when the dissipation parameters are larger than that of the ωrf, the interference intensity exhibits a fast attenuation behavior. As a comparison, the interference intensity in the absence of the dissipation is also studied. We conclude that the dissipation of the system can be evaluated by selecting the ωrf experimentally.
基金Supported by Natural Science Foundation of Shaanxi University of Science and Technology under Grant No.SUST-ZX08-27
文摘We investigate the Landau-Zener tunnelling of two-component Rose-Einstein condensates (BECs) in opticallattices.In the neighborhood of the Rrillouin zone edge,the system can be reduced to two coupled nonlinear two-levelmodels.From the models,we calculate the change of the tunnelling probability for each component with the linearsweeping rate.It is found that the probability for each component exhibits regular oscillating behavior for the largersweeping rate,but for smaller rate the oscillation is irregular.Moreover,the asymmetry of the tunnelling between thetwo components can be induced by the unbalanced initial populations or the inequality of the two self-interactions whenthe cross-interaction between the components exists.The result can not be found in the single component BECs.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11041003 and 60802087the Natural Science Foundation of Jiangsu Province under Grant No.BK2004119
文摘We present three families of exact matter-wave soliton solutions for an effective one-dimension twocomponent Bose-Einstein condensates(BECs) with tunable interactions,harmonic potential and gain or loss term. We investigate the dynamics of bright-bright solitons,bright-dark solitons and dark-dark solitons for the time-dependent expulsive harmonic trap potential,periodically modulated harmonic trap potential,and kinklike modulated harmonic trap potential.Through the Feshbach resonance,these dynamics can be realized in experiments by suitable control of time-dependent trap parameters,atomic interactions,and interaction with thermal cloud.
基金The project supported by National Natural Science Foundation of China under Grant Nos.90403034,90406017,and 60525417the State Key Basic Research Program of China under Nos.2005CB724508 and 2006CB921400
基金supported by the National Natural Science Foundation of China(Grant Nos.10974189,10675114,10675115,and 41075027)the Natural Science College Key Projects of Anhui Province,China(Grant No.KJ2011A040)
文摘The elementary excitation spectrum of a two-component Bose-Einstein condensate in different hyperfine states is obtained by Green's function method. It is found to have two branches. In the long wave-length limit, the two branches of the excitation spectrum are reduced to one phonon excitation and one single-particle excitation. The single-particle one has an energy gap. When the energy gap exists, we study the Landau critical velocity and the depletion of the condensate. With the obtained Green's functions, we calculate the structure factor of a two-component condensate. It is found that the static structure factor comprises only the branch of the phonon excitation and the single-particle excitation makes no contribution to the structure factor.