Macroscopic angular-momentum states of Bose-Einstein condensates in toroidal traps

Abstract

Abstract.- We study the stability of a rotating repulsive-atom Bose-Einstein condensate in a toroidal trap. The resulting macroscopic angular-momentum states with integer vorticity I spread radially, lowering rotational energies. These states are robust against vorticity-lowering decays, with estimated metastability barriers capable of sustaining large angular momenta ( / < 10) for typical parameters. We identify the centrifugally squashed /-dependent density profile as a possible signature of condensate rotation and superfluidity. Bose-Einstein condensates (BEC) of atoms in magnetic/optical traps have been the focus of intense recent activity [1-12]. The macroscopic phase-coherence of the BEC wave function was demonstrated by the observation of interference fringes in the overlap region of two freely spreading condensates [2], after the confining traps were switched off. However, the superfluid character of the interacting BEC is most clearly tested through the sustainability of super-currents. Non-destructive tests of phase-coherence and superfluidity, through Josephson-like effects have been proposed [6-9], including novel self-trapping phenomena and 7r-mode oscilla-tions [7,8]. A direct test of superfluidity in bulk superfluids/superconductors is the observation of quantized vortices [13,14] maintained by superflows. In multiply connected geometries (e.g.,