Quantum nucleation of vortices in the flow of superfluidHe4through an orifice

Abstract

Flow measurements in ultrapure ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ 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 ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ and strongly suggest that the underlying mechanism, the nucleation of vortex half-rings, is identical.