Reverse Rotation of Ring-Shaped Perturbation on Homogeneous Bose–Einstein Condensates

We numerically study the dynamics of rotating ring-shaped perturbation on two-dimensional homogeneous Bose–Einstein condensates, where a new ring-shaped structure with reverse rotation appears. The reversely rotating mode is directly caused by the existence of the plane wave (namely the homogeneous background). By the modified linear stability analysis method, we quantitatively predict the influence of the background's density on perturbation dynamics, including the velocity, amplitude, and frequency of the two rings. We construct an approximative solution to describe the short-lived dynamics of initial perturbation, which agrees well with our numerical results. Also, after the two rings separate, the transfer of atom number between them becomes linear, and the rate of transfer is impacted by the radial momentum of initial perturbation.