Vortices in a rotating two-component Bose–Einstein condensate with tunable interactions and harmonic potential

We consider a pair of coupled nonlinear Schrödinger equations modeling a rotating two-component Bose–Einstein condensate with tunable interactions and harmonic potential, with emphasis on the structure of vortex states by varying the strength of inter-component interaction, rotational frequency, and the aspect ratio of the harmonic potential. Our results show that the inter-component interaction greatly enhances the effect of rotation. For the case of isotropic harmonic potential and small inter-component interaction, the initial vortex structure remains unchanged. As the ratio of inter- to intra-component interactions increases, each component undergoes a transition from a vortex lattice (vortex line) in an isotropic (anisotropic) harmonic potential to an alternatively arranged stripe pattern, and eventually to the interwoven “serpentine” vortex sheets. Moreover, in the case of anisotropic harmonic potential the system can develop to a rotating droplet structure.     

Nonlinear resonance phenomenon of one-dimensional Bose–Einstein condensate under periodic modulation

We investigate the effect of an external periodic modulation on the one-dimensional （1D） Bose-Einstein conden- sate with harmonic trapping potential. By numerically solving the Gross-Pitaevskii equation with symplectic algorithm, the nonlinear resonance phenomenon is shown and the corresponding Fourier spectrum is given. The autoresonance phe- nomenon is also presented under almost periodic external modulation, and it shows that the condensate eventually evolves into quasi-periodic oscillation.     

Landau damping of collective mode in a quasi-two-dimensional repulsive Bose-Einstein condensate

We investigate the Landau damping of the collective mode in a quasi-two-dimension repulsive Bose-Einstein condensate by using the self-consistent time-dependent Hatree-Fock-Bogoliubov approximation and a complete and orthogonal eigenfunction set for the elementary excitation of the system.We calculate the three-mode coupling matrix element between the collective mode and the thermal excited quasi-particles and the Landau damping rate of the collective mode.We discuss the dependence of the Landau damping on temperature,on atom number in the condensate,on transverse trapping frequency and on the length of the condensate.The energy width of the collective mode is taken into account in our calculation.With little approximation,our theoretic calculation results agree well with the experimental ones and are helpful for deducing the damping mechanics and the inter-particle interaction.     

Exact analytical solutions of three-dimensional Gross-Pitaevskii equation with time-space modulation

By the generalized sub-equation expansion method and symbolic computation,this paper investigates the(3 + 1)dimensional Gross-Pitaevskii equation with time-and space-dependent potential,time-dependent nonlinearity,and gain or loss.As a result,rich exact analytical solutions are obtained,which include bright and dark solitons,Jacobi elliptic function solutions and Weierstrass elliptic function solutions.With computer simulation,the main evolution features of some of these solutions are shown by some figures.Nonlinear dynamics of a soliton pulse is also investigated under the different regimes of soliton management.     

Investigations of the exciton condensate

Recent experiments on quantum Hall bilayers in the vicinity of total filling factor 1 (ν_T=1) have revealed many exciting observations characteristic of a superfluidic exciton condensate. We report on our experimental work involving the ν_T=1 exciton condensate in independently contacted bilayer two-dimensional electron systems. We observe previously reported phenomena as a zero-bias resonant tunneling peak, a quantized Hall drag resistivity, and in counter-flow configuration, the near vanishing of both ρ_xx and ρ_xy resistivity components. At balanced electron densities in the layers, we find for both drag and counter-flow current configurations, thermally activated transport with a monotonic increase of the activation energy for d/ℓ_B<1.65 with activation energies up to 0.4 K. In the imbalanced system the activation energies show a striking asymmetry around the balance point, implying that the gap to charge excitations is considerably different in the separate layers that form the bilayer condensate. This indicates that the measured activation energy is neither the binding energy of the excitons, nor their condensation energy.     

Competition Among Three Coupled Bose-Einstein Condensates due to Potential Deviation

Three coupled Bose-Einstein condensates are investigated by the variational approach in finite potentials with potential deviation, and the effects of the potential deviation on dynamics of the three Bose-Einstein condensates are studied. The potential deviation leads to the shift of the stationary state, resets the stability condition, causes the population imbalance competition, and changes the switching and self-trapping effects on the Bose-Einstein condensates. The effect mechanism is demonstrated by performing a coordinate of classical particles moving in an effective potential field. The critical behaviors are analyzed, and are confirmed by evolution of the atom population imbalance ratio. PACS: 03.75.Fi, 32.80.Pj     

Fresnel Tomography: A Novel Approach to Wave-Function Reconstruction Based on the Fresnel Representation of Tomograms

We introduce a new type of tomographic probability distribution containing complete information about the density matrix (wave function) related to the Fresnel transform of the complex wave function. We elucidate the relation to the symplectic tomographic probability distribution. We present a multimode generalization of the Fresnel tomography and give examples of applications of the present approach. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 144, No. 2, pp. 384–393, August, 2005.     

Microvisual Study of Multiphase Gas Condensate Flow in Porous Media

Gas condensate reservoirs constitute a significant portion of hydrocarbon reserves worldwide. The liquid drop-out in these reservoirs may lead to recovery problems such as near wellbore permeability impairment and uncertainty in the actual location of the target condensate. Such technical issues can be addressed through improved understanding of the formation of condensate and the multiphase flow of gas/condensate/water in the reservoir as characterized by relative permeability curves. The appropriate relative permeability curves in turn can be used in reservoir simulators to assist in optimization of field development. This paper reports results of experiments conducted in micromodels, in support of possible core flow tests, using reservoir fluids under reservoir conditions. In particular, visualizations of condensate formation with and without connate water are presented and the differences between the two cases as well as the possible implications for the relative permeability measurements are discussed. Furthermore, the flow of gas and condensate at different force ratios (capillary and Bond numbers) are presented. It is postulated that a single dimensionless number may not be sufficient to characterize the multiphase flow in gas condensate reservoirs. The physical mechanisms occurring under various field conditions are examined in the light of these observations.     

Evolution of spin-dependent atomic wave packets in a harmonic potential

We have investigated theoretically the evolution of spin-dependent atomic wave packets in a harmonic magnetic trapping potential. For a Bose-condensed gas, which undergoes a Mott insulator transition and a spin-dependent transport, the atomic wavefunction can be described by an entangled single-atom state. Due to the confinement of the harmonic potential, the density distributions exhibit periodic decay and revival, which is different from the case of free expansion after switching off the combined harmonic and optical lattice potential.     

Wannier–Stark chaos of a Bose–Einstein condensate in 1D optical lattices

Using the idea of the macroscopic quantum wave function and the definition of the Melnikov chaos, we investigate the spatially chaotic features of a Bose–Einstein condensate (BEC) in a Wannier–Stark potential for the trivial phase and the non-trivial phase cases. The perturbed chaotic solutions are constructed, and the chaotic and unstable regions on the parameter space are illustrated. Numerical calculations to the spatial evolutions of the atomic number density and the energy density demonstrate the analytical results and exhibit the chaotic spatial distribution and energy distribution of the BEC atoms.