Quantum nucleation of vortices in the flow of superfluid He 4 through an orifice

摘要: Flow measurements in ultrapure He 4 through a micron-size orifice at millikelvin temperatures show, for the first time, the transition from thermal to quantum nucleation of nanometer-size vortices below a crossover temperature of 0.147 K. These observations establish the close relationship between this type of critical flow and negative-ion motion in superfluid He 4 and strongly suggest that the underlying mechanism, the nucleation of vortex half-rings, is identical.