Vortices in dipolar Bose–Einstein condensates in synthetic magnetic field

We study the formation of vortices in a dipolar Bose-Einstein condensate in a synthetic magnetic field by numerically solving the Gross-Pitaevskii equation. The formation process depends on the dipole strength, the rotating frequency, the potential geometry, and the orientation of the dipoles. We make an extensive comparison with vortices created by a rotating trap, especially focusing on the issues of the critical rotating frequency and the vortex number as a function of the rotating frequency. We observe that a higher rotating frequency is needed to generate a large number of vortices and the anisotropic interaction manifests itself as a perceptible difference in the vortex formation. Furthermore, a large dipole strength or aspect ratio also can increase the number of vortices effectively. In particular, we discuss the validity of the Feynman rule.

Trapped Bose-Einstein condensates in synthetic magnetic field

The rotational properties of Bose-Einstein condensates in a synthetic magnetic field are studied by numerically solving the Gross-Pitaevskii equation and comparing the results to those of condensates confined in a rotating trap. It appears to be more difficult to add a large angular momentum to condensates spun up by the synthetic magnetic field than by the rotating trap. However, strength- ening the repulsive interaction between atoms is an effective and realizable route to overcoming this problem and can at least generate vortex-lattice-like structures. In addition, the validity of the Feynman rule for condensates in the synthetic magnetic field is verified.

Nonreciprocal transition between two indirectly coupled energy levels

We propose a theoretical scheme to realize nonreciprocal transition between two energy levels that can not coupled directly.Suppose they are coupled indirectly by two auxiliary levels with a cyclic four-level configuration,and the four transitions in the cyclic configuration are controlled by external fields.The indirectly transition become nonreciprocal when the time reversal symmetry of the system is broken by the synthetic magnetic flux,i.e.,the total phase of the external driving fields through the cyclic four-level configuration.The nonreciprocal transition can be identified by the elimination of a spectral line in the spontaneous emission spectrum.Our work introduces a feasible way to observe nonreciprocal transition in a wide range of multi-level systems,including natural atoms or ions with parity symmetry.