Tao Yang | 西北大学 - Academia.edu (original) (raw)

Papers by Tao Yang

We study the dynamic behavior of a Bose-Einstein condensate (BEC) containing a dark soliton separ... more We study the dynamic behavior of a Bose-Einstein condensate (BEC) containing a dark soliton separately reflected from potential drops and potential barriers. It is shown that for a rapidly varying potential and in a certain regime of incident velocity, the quantum reflection probability displays the cosine of the deflection angle between the incident soliton and the reflected soliton, i.e., R(theta)simcos2thetaR(\theta) \sim \cos 2\thetaR(theta)simcos2theta. For a potential drop, R(theta)R(\theta)R(theta) is susceptible to the widths of potential drop up to the length of the dark soliton and the difference of the reflection rates between the orientation angle of the soliton theta=0\theta=0theta=0 and theta=pi/2\theta=\pi/2theta=pi/2, deltaRs\delta R_sdeltaRs, displays oscillating exponential decay with increasing potential widths. However, for a barrier potential, R(theta)R(\theta)R(theta) is insensitive for the potential width less than the decay length of the matter wave and deltaRs\delta R_sdeltaRs presents an exponential trend. This discrepancy of the reflectances in two systems is arisen from th...

In recent work it is shown that importance sampling can be avoided in the particle filter through... more In recent work it is shown that importance sampling can be avoided in the particle filter through an innovation structure inspired by traditional nonlinear filtering combined with Mean-Field Game formalisms [9], [19]. The resulting feedback particle filter (FPF) offers significant variance improvements; in particular, the algorithm can be applied to systems that are not stable. The filter comes with an up-front computational cost to obtain the filter gain. This paper describes new representations and algorithms to compute the gain in the general multivariable setting. The main contributions are, (i) Theory surrounding the FPF is improved: Consistency is established in the multivariate setting, as well as wellposedness of the associated PDE to obtain the filter gain. (ii) The gain can be expressed as the gradient of a function, which is precisely the solution to Poisson's equation for a related MCMC diffusion (the Smoluchowski equation). This provides a bridge to MCMC as well as to approximate optimal filtering approaches such as TD-learning, which can in turn be used to approximate the gain. (iii) Motivated by a weak formulation of Poisson's equation, a Galerkin finite-element algorithm is proposed for approximation of the gain. Its performance is illustrated in numerical experiments.

Journal of Physics B: Atomic, Molecular and Optical Physics

We study the dynamics of a doubly quantized vortex (DQV), created by releasing a ring-shaped Bose... more We study the dynamics of a doubly quantized vortex (DQV), created by releasing a ring-shaped Bose-Einstein condensate with quantized circulation into harmonic potential traps. It is shown that a DQV can be generated and exists stably in the middle of the ring-shaped condensate with the initial circulation s = 2 after released into the rotationally symmetric trap potential. For an asymmetric trap with a small degree of anisotropy the DQV initially splits into two singly quantized vortices and revives again but eventually evolves into two unit vortices due to the dynamic instability. For the degree of anisotropy above a critical value, the DQV is extremely unstably and decays rapidly into two singlet vortices. The geometry-dependent lifetime of the DQV and vortex-induced excitations are also discussed intensively.

By combining the algebraic Bethe ansatz and the off-diagonal Bethe ansatz, we investigate the sup... more By combining the algebraic Bethe ansatz and the off-diagonal Bethe ansatz, we investigate the supersymmetric t − J model with generic open boundaries. The eigenvalues of the transfer matrix are given in terms of an inhomogeneous T − Q relation, and the corresponding eigenstates are expressed in terms of nested Bethe states which have well-defined homogeneous limit. This exact solution provides basis for further analyzing the thermodynamic properties and correlation functions of the model.

We investigate the thermodynamic limit of the su(n)-invariant spin chain models with unparallel b... more We investigate the thermodynamic limit of the su(n)-invariant spin chain models with unparallel boundary fields. It is found that the contribution of the inhomogeneous term in the associated T –Q relation to the ground state energy does vanish in the thermodynamic limit. This fact allows us to calculate the boundary energy of the system. Taking the su(2) (or the XXX) spin chain and the su(3) spin chain as concrete examples , we have studied the corresponding boundary energies of the models. The method used in this paper can be generalized to study the thermodynamic properties and boundary energy of other high rank models with non-diagonal boundary fields.

The XXX Gaudin model with generic integrable open boundaries specified by the most general non-di... more The XXX Gaudin model with generic integrable open boundaries specified by the most general non-diagonal reflecting matrices is studied. Besides the inhomogeneous parameters, the associated Gaudin operators have six free parameters which break the U(1)-symmetry. With the help of the off-diagonal Bethe ansatz, we successfully obtained the eigenvalues of these Gaudin operators and the corresponding Bethe ansatz equations.

We introduce a long-range particle and spin interaction into the standard Bariev model and show t... more We introduce a long-range particle and spin interaction into the standard Bariev model and show that this interaction is equivalent to a phase shift in the kinetic term of the Hamiltonian. When the particles circle around the chain and across the boundary, the accumulated phase shift acts as a twist boundary condition with respect to the normal periodic boundary condition. This boundary phase term depends on the total number of particles in the system and also the number of particles in different spin states, which relates to the spin fluctuations in the system. The model is solved exactly via a unitary transformation by the coordinate Bethe ansatz. We calculate the Bethe equations and work out the energy spectrum with varying number of particles and spins.

Dynamics of vortex clusters is essential for understanding diverse superfluid phenomena. In this ... more Dynamics of vortex clusters is essential for understanding diverse superfluid phenomena. In this paper, we examine the dynamics of vortex quadrupoles in a trapped two-dimensional (2D) Bose-Einstein condensate. We find that the movement of these vortex-clusters fall into three distinct regimes which are fully described by the radial positions of the vortices in a 2D isotropic harmonic trap, or by the major radius (minor radius) of the elliptical equipotential lines decided by the vortex positions in a 2D anisotropic harmonic trap. In the " recombination " and " exchange " regimes the quadrupole structure maintains, while the vortices annihilate each other permanently in the " annihilation " regime. We find that the mechanism of the charge flipping in the " exchange " regime and the disappearance of the quadrupole structure in the " annihilation " regime are both through an intermediate state where two vortex dipoles connected through a soliton ring. We give the parameter ranges for these three regimes in coordinate space for a specific initial configuration and phase diagram of the vortex positions with respect to the Thomas-Fermi radius of the condensate. We show that the results are also applicable to systems with quantum fluctuations for the short-time evolution. Vortices could be observed in most realm of physics such as hydrodynamics, superfluids, optical fields and even cosmology. The dynamics of quantized vortices is essential for understanding diverse superfluid phenomena such as critical-current densities in superconductors 1 , quantum turbulence 2–6 and novel quantum phases 7–11 in superfluids. Vortices are also topological defects that play key roles in transport, dissipative and coherent properties 12–16 of superfluid systems. The pioneering work of Yarmchuk et al. in 1979 successfully located the ends of parallel vortex lines in superfluid Helium 17. The real-time dynamics of vortex lattice in type II super conductors was observed in 1992 18. Until 2006, direct observation of quantized vortex lines in superfluid Helium in arbitrary three-dimensional configurations has been achieved 19. The realization of Bose-Einstein condensates (BECs) provides an accessible and highly controllable platform for fundamental studies of superfluid vortex dynamics, and has been followed by various theoretical investigations and numerical analyses. It is remarkable that, comparing with other systems ruled by nonlinear Schrödinger equations , BECs are the ideal laboratory for finding these nonlinear excitations due to larger interaction strengths and easier tunable parameters. The size of vortex cores in a BEC is proportional to the healing length of the condensate,  ζ ρ = mg / 2 , where m is the mass of atoms, ρ is the density of the condensate in the absence of vortex, and g is the interatomic interaction strength. For given trap frequencies, g is proportional to the scattering length between atoms, which can be easily adjusted by using magnetic or optical Feshbach resonances 20–22. Due to the matter wave nature of condensates 23 , vortices can be detected in atomic interference. Matthews et al. 24 firstly demonstrated vortex production through an interference measurement, and later, Inouye et al. observed vortex phase singular-ities as dislocations in the interference fringes in BECs 25. As the size of the vortex cores in a trapped condensate is ordinarily several times smaller than the wavelength of light used for imaging, in experiments the condensates are usually allowed to expand to a point at which the vortex cores are large compared to the imaging resolution 24–30. Many works have been done to develop the vortex detection techniques and to understand vortex dynamics during the interference of BECs 25,31–36 , which is important for the applications of matter-wave interferometry. However, the direct, in situ observation of vortices in a trapped condensate without expansion was wachieved

The quantum τ 2-model with generic site-dependent inhomogeneity and arbitrary boundary fields is ... more The quantum τ 2-model with generic site-dependent inhomogeneity and arbitrary boundary fields is studied via the off-diagonal Bethe Ansatz method. The eigenvalues of the corresponding transfer matrix are given in terms of an inhomogeneous T −Q relation, which is based on the operator product identities among the fused transfer matrices and the asymptotic behavior of the transfer matrices. Moreover, the associated Bethe Ansatz equations are also obtained.

We investigate the effects of vortex interaction on the formation of interference patterns in a c... more We investigate the effects of vortex interaction on the formation of interference patterns in a coherent pair of two-dimensional Bose condensed clouds of ultra-cold atoms traveling in opposite directions subject to a harmonic trapping
potential. We identify linear and nonlinear regimes in the dipole oscillations of the
condensates according to the balance of internal and centre-of-mass energies of the
clouds. Simulations of the collision of two clouds each containing a vortex with different winding number (charge) were carried out in these regimes in order to investigate the creation of varying interference patterns. The interaction between different vortex type can be clearly distinguished by those patterns.

Physical Review A, 88(2013)043602

We investigate the effects of interatomic interactions and expansion on the distortion of interfe... more We investigate the effects of interatomic interactions and expansion on the distortion of interference fringes of a pair of initially well-separated, but coherent, condensate clouds trapped in a harmonic trap. The distortion of interference fringes, which can lead to the spontaneous formation of vortices in the atom clouds, depends crucially on two relevant parameters: the center-of-mass velocity and peak density of the initial state. We identify three qualitatively distinct regimes for the interfering condensates: collision, expansion, and merging, by the spatial and temporal features of the fringe spacings. Using a comprehensive set of numerical simulations based on the Gross-Pitaevskii equation, we specify the cross-overs between these regimes and propose the optimal the system parameters required for dynamical instabilities and vortex creation.

J. Phys. B: At. Mol. Opt. Phys. 46 (2013) 145307

We study the effect of quantum fluctuations on the dynamics of a quasi-one-dimensional Bose gas i... more We study the effect of quantum fluctuations on the dynamics of a quasi-one-dimensional Bose gas in an optical lattice at zero-temperature using the truncated Wigner approximation with a variety of basis sets for the initial fluctuation modes. The initial spatial distributions of the quantum fluctuations are very different when using a limited number of plane-wave (PW), simple-harmonic-oscillator (SHO) and self-consistently determined Bogoliubov (SCB) modes. The short-time transport properties of the Bose gas, characterized by the phase coherence in the PW basis are distinct from those gained using the SHO and SCB basis. The calculations using the SCB modes predict greater phase decoherence and stronger number fluctuations than the other choices. Furthermore, we observe that the use of PW modes overestimates the extent to which atoms are expelled from the core of the cloud, while the use of the other modes only breaks the cloud structure slightly which is in agreement with the experimental observations \cite{PRL.94.120403}.

J. Phys. B: At. Mol. Opt. Phys. 47 (2014) 035302

The quasiparticle excitation spectra of a Bose gas trapped in a highly anisotropic trap is studie... more The quasiparticle excitation spectra of a Bose gas trapped in a highly anisotropic trap is studied with respect to varying total number of particles by numerically solving the effective one-dimensional (1D) Gross-Pitaevskii (GP) equation proposed recently by Mateo \textit{et al.}. We obtain the static properties and Bogoliubov spectra of the system in the high energy domain. This method is computationally efficient and highly accurate for a condensate system undergoing a 1D to three-dimensional (3D) cigar-shaped transition, as is shown through a comparison our results with both those calculated by the 3D-GP equation and analytical results obtained in limiting cases. We identify the applicable parameter space for the effective 1D-GP equation and find that this equation fails to describe a system with large number of atoms. We also identify that the description of the transition from 1D Bose-Einstein condensate (BEC) to 3D cigar-shaped BEC using this equation is not smooth, which highlights the fact that for a finite value of aperp/asa_\perp/a_saperp/as the junction between the 1D and 3D crossover is not perfect.

Physica E 63(2014)160–164

In this work we use self-consistent method considering a two-dimensional electron gas system in t... more In this work we use self-consistent method considering a two-dimensional electron gas system in the integer quantum Hall regime, to calculate the temperature induced decay of incompressible stripes. There are two types of incompressible strips which can form in a Hall bar system by varying the electron density or magnetic field. We observe that the way of collapse of incompressible strips strongly depends on the type of them. With increasing temperature a bulk incompressible strip will decay from the middle and separate into two edge channels by a density ramp,while an incompressible edge channel reduces its size from both sides until vanishes.

Physical Review A, 87(2013)023603

We investigate the way in which the pattern of fringes in a coherent pair of two-dimensional Bose... more We investigate the way in which the pattern of fringes in a coherent pair of two-dimensional Bose condensed clouds of ultracold atoms traveling in opposite directions subject to a harmonic trapping potential can seed the irreversible formation of internal excitations in the clouds, notably solitons and vortices. We identify underdamped, overdamped, and critically damped regimes in the dipole oscillations of the condensates according to the balance of internal and center-of-mass energies of the clouds. We carry out simulations of the collision of two clouds with respect to different initial phase differences in these regimes to investigate the creation of internal excitations. We distinguish the behavior of this system from previous studies of quasi-one-dimensional BECs. In particular we note that the nature of the internal excitations is only essentially sensitive to an initial phase difference between the clouds in the overdamped regime.

We study the dynamic behavior of a Bose-Einstein condensate (BEC) containing a dark soliton separ... more We study the dynamic behavior of a Bose-Einstein condensate (BEC) containing a dark soliton separately reflected from potential drops and potential barriers. It is shown that for a rapidly varying potential and in a certain regime of incident velocity, the quantum reflection probability displays the cosine of the deflection angle between the incident soliton and the reflected soliton, i.e., R(theta)simcos2thetaR(\theta) \sim \cos 2\thetaR(theta)simcos2theta. For a potential drop, R(theta)R(\theta)R(theta) is susceptible to the widths of potential drop up to the length of the dark soliton and the difference of the reflection rates between the orientation angle of the soliton theta=0\theta=0theta=0 and theta=pi/2\theta=\pi/2theta=pi/2, deltaRs\delta R_sdeltaRs, displays oscillating exponential decay with increasing potential widths. However, for a barrier potential, R(theta)R(\theta)R(theta) is insensitive for the potential width less than the decay length of the matter wave and deltaRs\delta R_sdeltaRs presents an exponential trend. This discrepancy of the reflectances in two systems is arisen from th...

In recent work it is shown that importance sampling can be avoided in the particle filter through... more In recent work it is shown that importance sampling can be avoided in the particle filter through an innovation structure inspired by traditional nonlinear filtering combined with Mean-Field Game formalisms [9], [19]. The resulting feedback particle filter (FPF) offers significant variance improvements; in particular, the algorithm can be applied to systems that are not stable. The filter comes with an up-front computational cost to obtain the filter gain. This paper describes new representations and algorithms to compute the gain in the general multivariable setting. The main contributions are, (i) Theory surrounding the FPF is improved: Consistency is established in the multivariate setting, as well as wellposedness of the associated PDE to obtain the filter gain. (ii) The gain can be expressed as the gradient of a function, which is precisely the solution to Poisson's equation for a related MCMC diffusion (the Smoluchowski equation). This provides a bridge to MCMC as well as to approximate optimal filtering approaches such as TD-learning, which can in turn be used to approximate the gain. (iii) Motivated by a weak formulation of Poisson's equation, a Galerkin finite-element algorithm is proposed for approximation of the gain. Its performance is illustrated in numerical experiments.

Journal of Physics B: Atomic, Molecular and Optical Physics

We study the dynamics of a doubly quantized vortex (DQV), created by releasing a ring-shaped Bose... more We study the dynamics of a doubly quantized vortex (DQV), created by releasing a ring-shaped Bose-Einstein condensate with quantized circulation into harmonic potential traps. It is shown that a DQV can be generated and exists stably in the middle of the ring-shaped condensate with the initial circulation s = 2 after released into the rotationally symmetric trap potential. For an asymmetric trap with a small degree of anisotropy the DQV initially splits into two singly quantized vortices and revives again but eventually evolves into two unit vortices due to the dynamic instability. For the degree of anisotropy above a critical value, the DQV is extremely unstably and decays rapidly into two singlet vortices. The geometry-dependent lifetime of the DQV and vortex-induced excitations are also discussed intensively.

By combining the algebraic Bethe ansatz and the off-diagonal Bethe ansatz, we investigate the sup... more By combining the algebraic Bethe ansatz and the off-diagonal Bethe ansatz, we investigate the supersymmetric t − J model with generic open boundaries. The eigenvalues of the transfer matrix are given in terms of an inhomogeneous T − Q relation, and the corresponding eigenstates are expressed in terms of nested Bethe states which have well-defined homogeneous limit. This exact solution provides basis for further analyzing the thermodynamic properties and correlation functions of the model.

We investigate the thermodynamic limit of the su(n)-invariant spin chain models with unparallel b... more We investigate the thermodynamic limit of the su(n)-invariant spin chain models with unparallel boundary fields. It is found that the contribution of the inhomogeneous term in the associated T –Q relation to the ground state energy does vanish in the thermodynamic limit. This fact allows us to calculate the boundary energy of the system. Taking the su(2) (or the XXX) spin chain and the su(3) spin chain as concrete examples , we have studied the corresponding boundary energies of the models. The method used in this paper can be generalized to study the thermodynamic properties and boundary energy of other high rank models with non-diagonal boundary fields.

The XXX Gaudin model with generic integrable open boundaries specified by the most general non-di... more The XXX Gaudin model with generic integrable open boundaries specified by the most general non-diagonal reflecting matrices is studied. Besides the inhomogeneous parameters, the associated Gaudin operators have six free parameters which break the U(1)-symmetry. With the help of the off-diagonal Bethe ansatz, we successfully obtained the eigenvalues of these Gaudin operators and the corresponding Bethe ansatz equations.

We introduce a long-range particle and spin interaction into the standard Bariev model and show t... more We introduce a long-range particle and spin interaction into the standard Bariev model and show that this interaction is equivalent to a phase shift in the kinetic term of the Hamiltonian. When the particles circle around the chain and across the boundary, the accumulated phase shift acts as a twist boundary condition with respect to the normal periodic boundary condition. This boundary phase term depends on the total number of particles in the system and also the number of particles in different spin states, which relates to the spin fluctuations in the system. The model is solved exactly via a unitary transformation by the coordinate Bethe ansatz. We calculate the Bethe equations and work out the energy spectrum with varying number of particles and spins.

Dynamics of vortex clusters is essential for understanding diverse superfluid phenomena. In this ... more Dynamics of vortex clusters is essential for understanding diverse superfluid phenomena. In this paper, we examine the dynamics of vortex quadrupoles in a trapped two-dimensional (2D) Bose-Einstein condensate. We find that the movement of these vortex-clusters fall into three distinct regimes which are fully described by the radial positions of the vortices in a 2D isotropic harmonic trap, or by the major radius (minor radius) of the elliptical equipotential lines decided by the vortex positions in a 2D anisotropic harmonic trap. In the " recombination " and " exchange " regimes the quadrupole structure maintains, while the vortices annihilate each other permanently in the " annihilation " regime. We find that the mechanism of the charge flipping in the " exchange " regime and the disappearance of the quadrupole structure in the " annihilation " regime are both through an intermediate state where two vortex dipoles connected through a soliton ring. We give the parameter ranges for these three regimes in coordinate space for a specific initial configuration and phase diagram of the vortex positions with respect to the Thomas-Fermi radius of the condensate. We show that the results are also applicable to systems with quantum fluctuations for the short-time evolution. Vortices could be observed in most realm of physics such as hydrodynamics, superfluids, optical fields and even cosmology. The dynamics of quantized vortices is essential for understanding diverse superfluid phenomena such as critical-current densities in superconductors 1 , quantum turbulence 2–6 and novel quantum phases 7–11 in superfluids. Vortices are also topological defects that play key roles in transport, dissipative and coherent properties 12–16 of superfluid systems. The pioneering work of Yarmchuk et al. in 1979 successfully located the ends of parallel vortex lines in superfluid Helium 17. The real-time dynamics of vortex lattice in type II super conductors was observed in 1992 18. Until 2006, direct observation of quantized vortex lines in superfluid Helium in arbitrary three-dimensional configurations has been achieved 19. The realization of Bose-Einstein condensates (BECs) provides an accessible and highly controllable platform for fundamental studies of superfluid vortex dynamics, and has been followed by various theoretical investigations and numerical analyses. It is remarkable that, comparing with other systems ruled by nonlinear Schrödinger equations , BECs are the ideal laboratory for finding these nonlinear excitations due to larger interaction strengths and easier tunable parameters. The size of vortex cores in a BEC is proportional to the healing length of the condensate,  ζ ρ = mg / 2 , where m is the mass of atoms, ρ is the density of the condensate in the absence of vortex, and g is the interatomic interaction strength. For given trap frequencies, g is proportional to the scattering length between atoms, which can be easily adjusted by using magnetic or optical Feshbach resonances 20–22. Due to the matter wave nature of condensates 23 , vortices can be detected in atomic interference. Matthews et al. 24 firstly demonstrated vortex production through an interference measurement, and later, Inouye et al. observed vortex phase singular-ities as dislocations in the interference fringes in BECs 25. As the size of the vortex cores in a trapped condensate is ordinarily several times smaller than the wavelength of light used for imaging, in experiments the condensates are usually allowed to expand to a point at which the vortex cores are large compared to the imaging resolution 24–30. Many works have been done to develop the vortex detection techniques and to understand vortex dynamics during the interference of BECs 25,31–36 , which is important for the applications of matter-wave interferometry. However, the direct, in situ observation of vortices in a trapped condensate without expansion was wachieved

The quantum τ 2-model with generic site-dependent inhomogeneity and arbitrary boundary fields is ... more The quantum τ 2-model with generic site-dependent inhomogeneity and arbitrary boundary fields is studied via the off-diagonal Bethe Ansatz method. The eigenvalues of the corresponding transfer matrix are given in terms of an inhomogeneous T −Q relation, which is based on the operator product identities among the fused transfer matrices and the asymptotic behavior of the transfer matrices. Moreover, the associated Bethe Ansatz equations are also obtained.

We investigate the effects of vortex interaction on the formation of interference patterns in a c... more We investigate the effects of vortex interaction on the formation of interference patterns in a coherent pair of two-dimensional Bose condensed clouds of ultra-cold atoms traveling in opposite directions subject to a harmonic trapping
potential. We identify linear and nonlinear regimes in the dipole oscillations of the
condensates according to the balance of internal and centre-of-mass energies of the
clouds. Simulations of the collision of two clouds each containing a vortex with different winding number (charge) were carried out in these regimes in order to investigate the creation of varying interference patterns. The interaction between different vortex type can be clearly distinguished by those patterns.

Physical Review A, 88(2013)043602

We investigate the effects of interatomic interactions and expansion on the distortion of interfe... more We investigate the effects of interatomic interactions and expansion on the distortion of interference fringes of a pair of initially well-separated, but coherent, condensate clouds trapped in a harmonic trap. The distortion of interference fringes, which can lead to the spontaneous formation of vortices in the atom clouds, depends crucially on two relevant parameters: the center-of-mass velocity and peak density of the initial state. We identify three qualitatively distinct regimes for the interfering condensates: collision, expansion, and merging, by the spatial and temporal features of the fringe spacings. Using a comprehensive set of numerical simulations based on the Gross-Pitaevskii equation, we specify the cross-overs between these regimes and propose the optimal the system parameters required for dynamical instabilities and vortex creation.

J. Phys. B: At. Mol. Opt. Phys. 46 (2013) 145307

We study the effect of quantum fluctuations on the dynamics of a quasi-one-dimensional Bose gas i... more We study the effect of quantum fluctuations on the dynamics of a quasi-one-dimensional Bose gas in an optical lattice at zero-temperature using the truncated Wigner approximation with a variety of basis sets for the initial fluctuation modes. The initial spatial distributions of the quantum fluctuations are very different when using a limited number of plane-wave (PW), simple-harmonic-oscillator (SHO) and self-consistently determined Bogoliubov (SCB) modes. The short-time transport properties of the Bose gas, characterized by the phase coherence in the PW basis are distinct from those gained using the SHO and SCB basis. The calculations using the SCB modes predict greater phase decoherence and stronger number fluctuations than the other choices. Furthermore, we observe that the use of PW modes overestimates the extent to which atoms are expelled from the core of the cloud, while the use of the other modes only breaks the cloud structure slightly which is in agreement with the experimental observations \cite{PRL.94.120403}.

J. Phys. B: At. Mol. Opt. Phys. 47 (2014) 035302

The quasiparticle excitation spectra of a Bose gas trapped in a highly anisotropic trap is studie... more The quasiparticle excitation spectra of a Bose gas trapped in a highly anisotropic trap is studied with respect to varying total number of particles by numerically solving the effective one-dimensional (1D) Gross-Pitaevskii (GP) equation proposed recently by Mateo \textit{et al.}. We obtain the static properties and Bogoliubov spectra of the system in the high energy domain. This method is computationally efficient and highly accurate for a condensate system undergoing a 1D to three-dimensional (3D) cigar-shaped transition, as is shown through a comparison our results with both those calculated by the 3D-GP equation and analytical results obtained in limiting cases. We identify the applicable parameter space for the effective 1D-GP equation and find that this equation fails to describe a system with large number of atoms. We also identify that the description of the transition from 1D Bose-Einstein condensate (BEC) to 3D cigar-shaped BEC using this equation is not smooth, which highlights the fact that for a finite value of aperp/asa_\perp/a_saperp/as the junction between the 1D and 3D crossover is not perfect.

Physica E 63(2014)160–164

In this work we use self-consistent method considering a two-dimensional electron gas system in t... more In this work we use self-consistent method considering a two-dimensional electron gas system in the integer quantum Hall regime, to calculate the temperature induced decay of incompressible stripes. There are two types of incompressible strips which can form in a Hall bar system by varying the electron density or magnetic field. We observe that the way of collapse of incompressible strips strongly depends on the type of them. With increasing temperature a bulk incompressible strip will decay from the middle and separate into two edge channels by a density ramp,while an incompressible edge channel reduces its size from both sides until vanishes.

Physical Review A, 87(2013)023603

We investigate the way in which the pattern of fringes in a coherent pair of two-dimensional Bose... more We investigate the way in which the pattern of fringes in a coherent pair of two-dimensional Bose condensed clouds of ultracold atoms traveling in opposite directions subject to a harmonic trapping potential can seed the irreversible formation of internal excitations in the clouds, notably solitons and vortices. We identify underdamped, overdamped, and critically damped regimes in the dipole oscillations of the condensates according to the balance of internal and center-of-mass energies of the clouds. We carry out simulations of the collision of two clouds with respect to different initial phase differences in these regimes to investigate the creation of internal excitations. We distinguish the behavior of this system from previous studies of quasi-one-dimensional BECs. In particular we note that the nature of the internal excitations is only essentially sensitive to an initial phase difference between the clouds in the overdamped regime.