Hongwei Xiong

Electromagnetically induced transparency in multi-level cascade scheme of cold rubidium atoms

We report an experimental investigation of electromagnetically induced transparency in a multi-level cascade system of cold Rb-85 atoms. The absorption spectral profiles of the probe light and their dependence on the intensity of the coupling laser were investigated. The experimental measurements agree with the theoretical calculations

Canonical statistics of trapped ideal and interacting Bose gases

The mean ground-state occupation number and condensate fluctuations of interacting and noninteracting Bose gases confined in a harmonic trap are considered by using a canonical ensemble approach. To obtain the mean ground-state occupation number and the condensate fluctuations, an analytical description for the probability distribution function of the condensate is provided directly starting from the analysis of the partition function of the system. For the ideal Bose gas, the probability distribution function is found to be a Gaussian one for the case of the harmonic trap. For the interacting Bose gas, using a unified approach the condensate fluctuations are calculated based on the lowest-order perturbation method and on Bogoliubov theory. It is found that the condensate fluctuations based on the lowest-order perturbation theory follow the law

Interference patterns of Bose-condensed gases in a two-dimensional optical lattice

〈{\ensuremath{\delta}}^{2}{N}_{0}〉\ensuremath{\sim}N,

Critical correlations in an ultra-cold Bose gas revealed by means of a temporal Talbot–Lau interferometer

while the fluctuations based on Bogoliubov theory behave as

Atomic quantum corrals for Bose-Einstein condensates

{N}^{4/3}.

Statistical properties of interacting Bose gases in quasi-two-dimensional harmonic traps

For a Bose-condensed gas confined in a magnetic trap and in a two-dimensional (2D) optical lattice, the non-uniform distribution of atoms in different lattice sites is considered based on the Gross?Pitaevskii equation. A propagator method is used to investigate the time evolution of 2D interference patterns after (i) only the optical lattice is switched off, and (ii) both the optical lattice and the magnetic trap are switched off. An analytical description on the motion of side peaks in the interference patterns is presented by using the density distribution in a momentum space.

Fluctuations of the condensate in ideal and interacting Bose gases

The transition from a thermal cloud to a Bose-Einstein condensate (BEC) in an interacting ultra-cold Bose gas is a prototype in a universality class of diverse phase transitions. For a trapped ultra-cold Bose gas, we were able to study the critical regime both above and below the critical temperature with a Talbot-Lau interferometer, observing a peak in the correlation length. From this peak, we managed to determine the universal critical exponents for this phase transition as well as the finite-size and interaction corrections to the critical temperature. The results are all in quantitative agreement with theory. This work demonstrates the potential application of the Talbot-Lau interferometer to a wide range of critical phase transitions in ultra-cold atomic gases.

Observation of diffraction phases in matter-wave scattering

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.

Observation of quantum dynamical oscillations of ultracold atoms in the F and D bands of an optical lattice

We investigate the interference pattern evolution process for a coherent array of Bose–Einstein condensates in a magnetic trap after the optical lattices are switched off. It is shown that there is a decay and revival of the density oscillation for the condensates confined in the magnetic trap. We find that, due to the confinement of the magnetic trap, the interference effect is much stronger than that found in the experiment performed by Pedri et al (Pedri P et al 2001 Phys. Rev. Lett. 87 220401), where the magnetic trap is also switched off. The interaction correction to the interference effect is also discussed for the density distribution of the central peak.