Anomalous rotational properties of Bose-Einstein condensates in asymmetrictraps - art. no. 013602

We study the rotational properties of a Bose-Einstein condensate confined i n a rotating harmonic trap for different trap anisotropies. With simple arg uments, we obtain the velocity field of the quantum fluid for condensates w ith or without a centered vortex. While the bosons describe open spiraling trajectories, on the frame of reference of the rotating trap, the fluid mov es against the trap's rotation. We also find expressions for the angular mo mentum of linear and Thomas-Fermi solutions for a vortexless state. In thes e two limits we find the same analytic relation between the shape of the cl oud and the rotation speed. Our predictions are supported by numerical simu lations of the mean-field Gross-Pitaevskii model and by current experiments with rotating Bose-Einstein condensates (K. W. Madison, F. Chevy, V. Breti n, and J. Dalibard, e-print cond-mat/0101051).