On the vortex stability in BEC

Abstract

The exotic quantum phenomenon of Bose–Einstein condensation (BEC) is the key ingredient in a new type of laser that emits atoms rather than photons, and that promises to revolutionize atom optics. In this paper, we consider the possibility of stable angular momentum transfer by an atom laser beam which should be more useful in various applications than a circularly polarized photon laser. The most promising way to assign the initial angular momentum is the outcoupling from the BEC cloud in a vortex state. However, the question of the vortex stability (metastability) arises as well as stability of the beam angular momentum. Here we propose a method for the solution of this problem by developing a quasi-hydrodynamic approach to the condensate with account of its interaction with the non-condensed atoms. Using the concept of local hydrodynamical invariants, we further derive the necessary conditions for the beam, such that the initial angular momentum is transferred conservatively. Both continuous and pulsed schemes are considered.