Quantum Phase Slippage in Superfluid 4He

Abstract

The concept of phase slippage was introduced in superfluid physics by Anderson in 1966. Direct experimental evidence of this basic phenomenon was looked for unsuccessfully for decades. We describe observations of highly reproducible, discrete dissipation events in the flow of superfluid 4He through a microscopic orifice. These events occur at a rate given by the a.c. Josephson equation and they are shown to correspond to the creation of trapped quantised circulation. The onset threshold of the critical velocity at which these events occur is found to be strongly altered by minute traces of 3He impurities and to vary with temperature as 1 - T/T0 with T0 = 2.46 K from 1.2 K down to 5 mK. We interpret these events as slips of the quantum-mechanical phase difference across the orifice by 2π in the sense of Anderson.