PHASE-SLIP PHENOMENA IN SUPERFLUID-HELIUM

The phase of the quantum wave function describing a superfluid is a macroscopic variable. This statement, first made by F. London, has implications on the flow properties of helium through small orifices. These implications were explored in 1966 by P.W. Anderson who coined the word phase slippage. But it is only recently that phase slips have been observed experimentally in conjunction with a search for the analogs of the Josephson effects in superfluids. We shall review the present experimental situation, with an emphasis on the problem of the nucleation of vortices in superfluid He-4 and on their trajectories to complete a slip by 2pi across the orifice.