Effective interactions between two impurities in quasi-two-dimensional dipolar Bose–Einstein condensates

We investigate the effective interaction between two heavy impurities immersed in a quasi-twodimensional dipolar Bose-Einstein condensate via a variation approach. We show that the mediated interaction is highly tunable via the contact and the dipole-dipole interactions between the background gas atoms. Interestingly, the mediated interaction potential may become an oscillating function of inter-impurity distance when roton excitation emerges under sufficiently strong dipolar interaction. Our system therefore provides an efficient way for tuning the mediated interaction between impurities.     

Dynamics of quantum vortices in a quasi-two-dimensional Bose–Einstein condensate with two “holes”

The dynamics of interacting quantum vortices in a quasi-two-dimensional spatially inhomogeneous Bose–Einstein condensate, whose equilibrium density vanishes at two points of the plane with a possible presence of an immobile vortex with a few circulation quanta at each point, has been considered in a hydrodynamic approximation. A special class of density profiles has been chosen, so that it proves possible to calculate analytically the velocity field produced by point vortices. The equations of motion have been given in a noncanonical Hamiltonian form. The theory has been generalized to the case where the condensate forms a curved quasi-two-dimensional shell in the three-dimensional space.     

Bragg spectroscopy and superradiant Rayleigh scattering in a Bose–Einstein condensate

Two sets of studies concerning the interaction of off-resonant light with a sodium Bose–Einstein condensate are described. In the first set, properties of a Bose–Einstein condensate were studied using Bragg spectroscopy. The high momentum and energy resolution of this method allowed a spectroscopic measurement of the mean-field energy and of the intrinsic momentum distribution of the condensate. Depending on the momentum transfer, both the phonon regime as well as the free-particle regime could be explored. In the second set of studies, the cigar-shaped condensate was exposed to a single off-resonant laser beam and highly directional scattering of light and atoms was observed. This collective light scattering was caused by the long coherence time of the quasi-particles in the condensate and resulted in a new form of matter wave amplification. Received: 26 June 1999 / Revised version: 21 September 1999 / Published online: 10 November 1999     

Domain walls and their interactions in a two-component Bose–Einstein condensate

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.     

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.     

Dynamical coupling between a Bose–Einstein condensate and a cavity optical lattice

A Bose–Einstein condensate is dispersively coupled to a single mode of an ultra-high finesse optical cavity. The system is governed by strong interactions between the atomic motion and the light field even at the level of single quanta. While coherently pumping the cavity mode the condensate is subject to the cavity optical lattice potential whose depth depends nonlinearly on the atomic density distribution. We observe optical bistability already below the single photon level and strong back-action dynamics which tunes the coupled system periodically out of resonance.     

Spinor molecule in atomic Bose–Einstein condensate

We have performed two-photon photoassociation experiments in atomic Bose–Einstein condensate (BEC) of ⁸⁷Rb with spin degree of freedom which is created by all-optical method with CO₂ lasers. The spinor character of the molecules has been revealed by the photoassociation spectrum with a new structure. The hyperfine structure of the molecules near the dissociation limit is identified by observations of the Zeeman and AC-Stark effects of the molecules. The molecules have been spin-selectively probed by the use of the light shift. This result would open the new possibility of research on novel spinor molecular BEC.     

Spatial structure of a Bose–Einstein condensate in a combined trap

We study the spatial structure of a Bose–Einstein condensate(BEC) with a space-dependent s-wave scattering length in a combined trap. There exists a space-dependent nonlinear atomic current in the system. The atomic current has an important influence on the spatial structure of the BEC. Research findings reveal that a large chemical potential can effectively suppress the chaotic spatial structure in the BEC system. Due to the large chemical potential, a strong atomic current is necessary to make...     

Vector kink-dark complex solitons in a three-component Bose–Einstein condensate

We investigate kink-dark complex solitons(KDCSs) in a three-component Bose–Einstein condensate(BEC) with repulsive interactions and pair-transition(PT) effects. Soliton profiles critically depend on the phase differences between dark solitons excitation elements. We report a type of kink-dark soliton profile which shows a droplet-bubble-droplet with a density dip, in sharp contrast to previously studied bubble-droplets. The interaction between two KDCSs is further investigated. It demonstrates some striking particle transition behaviours during their collision processes, while soliton profiles survive after the collision. Additionally, we exhibit the state transition dynamics between a kink soliton and a dark soliton. These results suggest that PT effects can induce more abundant complex solitons dynamics in multi-component BEC.     

Composite solitons in SU(3) spin–orbit-coupling Bose gases

We study solitons in a spin-1 Bose–Einstein condensates with SU(3) spin–orbit coupling. We obtain the ground state and the metastable solution for solitons with attractive interactions by the imaginary-time evolution method. Compared with the SU(2) spin–orbit coupling, it is found that the solitons in SU(3) spin–orbit coupling show a new feature due to breaking the symmetry. The solitons called the composite solitons have mixing manifolds of ferromagnetic and antiferromagnetic states. This has stimulated people to study the topological excitation properties of SU(3) spin–orbit coupling and it is expected to find new quantum phases.     

Transfer of entangled state, entanglement swapping and quantum information processing via the Rydberg blockade

We provide a scheme with which the transfer of the entangled state and the entanglement swapping can be realized in a system of neutral atoms via the Rydberg blockade. Our idea can be extended to teleport an unknown atomic state. According to the latest theoretical research of the Rydberg excitation and experimental reports of the Rydberg blockade effect in quantum information processing, we discuss the experimental feasibility of our scheme.