Rayleigh-Taylor instability and vortex rings in coupled Gross-Pitaevskii equations.

The Rayleigh-Taylor instability is a gravitational instability in two fluids where the heavier fluid is set over the lighter fluid. The instability occurs both in classical fluids and quantum fluids. We numerically study the Rayleigh-Taylor instability using coupled Gross-Pitaevskii equations for two-component Bose-Einstein condensates. We carry out numerical simulations that the heavier component is set in a torus initially which is surrounded by the lighter component. When the torus falls, the Rayleigh-Taylor instability develops and a sagging pattern appears. This instability is investigated for the two cases with and without a vortex ring inside the torus. We find that a vortex ring suppresses the instability when the radius of the torus is small.