Engineering topics

Hongwei, Xiong

Publications and source records attributed to Hongwei, Xiong.

4 records

DOE OSTI2010

Quantum coherence for Bose-Einstein condensates induced by an imaginary potential

The single-body Schroedinger equation with complex potentials has been studied intensively. In this work, we investigate the dynamical process for Bose-Einstein condensed gases, based on the many-body Schroedinger equation with complex potentials. It is shown that a weakly imaginary periodic potential may induce perfect quantum coherence between different condensates, even without considering interatomic interactions. This imaginary-potential-induced quantum coherence may be tested with present experimental techniques. We also consider the quantum coherence in the presence of both the imaginary periodic potential and interatomic interactions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2010

Hidden vortices in a Bose-Einstein condensate in a rotating double-well potential

We study vortex formation in a Bose-Einstein condensate in a rotating double-well potential. In addition to the ordinary quantized vortices and elusive ghost vortices, 'hidden' vortices are found distributed along the central barrier. These hidden vortices are invisible like ghost vortices but carry angular momentum. Moreover, their core size is not given by the healing length, but is strongly influenced by the external potential. We find that the Feynman rule can be well satisfied only after including the hidden vortices. There is no critical rotation frequency for the formation of hidden vortices while there is one for the formation of ordinary visible vortices. Hidden vortices can be revealed in the free expansion of Bose-Einstein condensates. In addition, the hidden vortices in a Bose-Einstein condensate can appear in other external potentials, such as a rotating anisotropic toroidal trap.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2010

Phase transition to Bose-Einstein condensation for a bosonic gas confined in a combined trap

We present a study of phase transition to macroscopic superfluidity for an ultracold bosonic gas confined in a combined trap formed by a one-dimensional optical lattice and a harmonic potential, focusing on the critical temperature of this system and the interference patterns of the Bose gas released from the combined trap. Based on a semiclassical energy spectrum, we develop an analytic approximation for the critical temperature T{sub c}, and compare the analytic results with that obtained by numerical computations. For finite temperatures below T{sub c}, we calculate the interference patterns for both the normal gas and the superfluid gas. The total interference pattern shows a feature of 'peak on a peak'. As a comparison, we also present the experimentally observed interference patterns of {sup 87}Rb atoms released from a one-dimensional optical lattice system in accord with our theoretical model. Our observations are consistent with the theoretical results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2010

Atomic quantum corrals for Bose-Einstein condensates

We consider the dynamics of Bose-Einstein condensates in a corral-like potential. Compared to the electronic quantum corrals, the atomic quantum corrals have the advantages of allowing direct and convenient observation of the wave dynamics, together with adjustable interaction strength. Our numerical study shows that these advantages not only allow exploration of the rich dynamical structures in the density distribution but also make the corrals useful in many other aspects. In particular, the corrals for atoms can be arranged into a stadium shape for the experimental visualization of quantum chaos, which has been elusive with electronic quantum corrals. The density correlation is used to describe quantitatively the dynamical quantum chaos. Furthermore, we find that the interatomic interaction can greatly enhance the dynamical quantum chaos, for example, inducing a chaotic behavior even in circle-shaped corrals.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗