We study the quantum dynamics of a model for a vortex in a Bose gas with
repulsive interactions in an anisotropic, harmonic trap. By solving the
Schr\"odinger equation numerically, we show that the circulation of the vortex
can undergo periodic reversals by quantum-mechanical tunneling. With increasing
interaction strength or particle number, vortices become increasingly stable,
and the period for reversals increases. Tunneling between vortex and antivortex
states is shown to be described to a good approximation by a superposition of
vortex and antivortex states (a Schr\"odinger cat state), rather than the
mean-field state, and we derive an analytical expression for the oscillation
period. The problem is shown to be equivalent to that of the two-site Bose
Hubbard model with attractive interactions.Comment: 5 pages, 5 figures; published in Phys. Rev. A, Rapid Communication