Nucleation of quantized vortex rings in He4 nanodroplets

Whereas most of the phenomena associated with superfluidity have been observed in finite-size helium systems, the nucleation of quantized vortices has proven elusive. Here we show using timedependent density functional simulations that the solvation of a Ba+ ion created by photoionization of neutral Ba at the surface of a 4He nanodroplet leads to the nucleation of a quantized ring vortex. The vortex is nucleated on a 10 ps timescale at the equator of a solid-like solvation structure that forms around the Ba+ ion. The process is expected to be quite general and very efficient under standard experimental conditions.