Rotational States of Bose Gases with Attractive Interactions in Anharmonic Traps

A rotated and harmonically trapped Bose gas with attractive interactions is expected to either remain stationary or escape from the trap. Here we report that, on the contrary, in an anharmonic trapping potential the Bose gas with attractive interactions responds to external rotation very differently, namely, through center-of-mass motion or by formation of vortices.

Figure 1

Dependence of angular momentum on rotational frequency. The thick solid lines indicate the variational result, and the thinner lines represent the fully numerical results for the cases $N=15$ (full line), 10 (dashed line), and 8 (dotted line).

Figure 2

The solid lines represent the boundaries between the three phases (vortex phase, center-of-mass rotation, and unstable phase) for the case of one quantum of angular momentum per particle, $L_z=N\hslash$. The dashed lines represent the case $L_z=2N\hslash$. The dotted line is the boundary between the stable and unstable regimes for a nonrotating cloud. The lines are calculated in the variational scheme. The dot-dashed line is the perturbative result.