Rossby waves in rapidly rotating Bose–Einstein condensates

We predict and describe a new collective mode in rotating Bose–Einstein condensates, which is very similar to Rossby waves in geophysics. In the regime of fast rotation, the Coriolis force dominates the dynamics and acts as a restoring force for acoustic-drift waves along the condensate. We derive a nonlinear equation that includes the effects of both zero-point pressure and inhomogeneity of the gas. It is shown that such waves have negative phase speed, propagating in the opposite sense of the rotation. We discuss different equilibrium configurations and compare them to those resulting from the Thomas–Fermi approximation. The rotation of Bose–Einstein condensates (BECs) has attracted much attention recently, both theoretically and experimentally [1, 2]. Due to the superfluid character of the BEC, the effects of rotation are quite different from those observed in a normal fluid and its properties strongly depend on the effects of confinement. The pioneering experiments based on both the phase imprinting [3] and the rotating laser beam [4, 5] techniques independently confirmed the nucleation of quantized vortices, which is a clear manifestation of the superfluid properties of the condensate. Since then, much effort has been made to understand the dynamics of the rotating BEC [6] and, in particular, the mechanisms of vortex nucleation [7, 8]. In particular, interesting features of quantized vortices in BECs of alkali atoms are related to the formation of vortex arrays, where singly quantized vortices are typically arranged in highly regular triangular lattices, similar to the Abrikosov lattice for superconductors. Such a configuration is possible only when a sufficient amount of angular momentum is effectively transferred to the system, 4 Author to whom any correspondence should be addressed. New Journal of Physics 12 (2010) 093001 1367-2630/10/093001+08$30.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft