Bose–Einstein condensation in nonuniform rotation

In this work, we study Bose–Einstein condensation in a system, where the rotation frequency decreases radially from the center. The system is described by a modified Gross–Pitaevskii equation that includes a nonuniform rotation term controlled by a parameter [Formula: see text], with the length scale of the rotation variation fixed relative to the healing length. The results show behavior distinctly different from the uniformly rotating condensate. In the uniform case, a triangular vortex lattice forms, whereas here we observe that above a critical value [Formula: see text] the vortices arrange themselves into a circular ring-shaped pattern near the boundary. Below [Formula: see text], the vortex configuration is disordered, lacking both triangular symmetry and a clear ring structure. The energy and chemical potential exhibit a sharp change at [Formula: see text], signaling a structural phase transition. A phase diagram is presented for the transition from the disordered to the ring-shaped vortex arrangement. The findings are discussed in the context of current experiments on synthetic gauge fields and structured rotation.