Multiple quantum phase slips in superfluid4He

Phase slips by 2 in the critical flow of superfluid 4He through an orifice have been known to exist for some time. Besides these small, regular events, large and precipitous drops of the velocity which may cause up to a full collapse of the flow through the orifice have been observed by a number of authors. We have found that collapses are robust and repeatable features during the same cool-down and correspond to events involving n quantized vortices. They depend on temperature, pressure, 3He content and resonator drive level. At a given pressure, their appearance is governed solely by the magnitude of the superfluid velocity vs.