Observation of Quantized Circulation in Superfluid Helium

An experimental study has been made of the circulation of the superfluid component of liquid helium II around a fine wire. The method used was that of Vinen, in which the circulation is measured by means of the influence it has on the transverse vibrations of the wire. The present work extends Vinen's original work in several ways. Measurements were made over a range of temperatures from 1.2 to 1.9°K and a range of wire diameters from 25 to 100 μ. In addition, measurements of the direction of the apparent circulation were made as well as of the magnitude. The experiments have two principal results. The first is that motion of the superfluid around the wire could persist for many hours after any motion of the containing vessel had stopped. However, this motion was not steady; smooth changes in apparent circulation could take place throughout an experimental run, changes which could include reversals in direction. The second principal result is that the apparent circulation tended to show markedly greater stability at the anticipated quantum levels than at other values. Long periods of stability were observed at the levels of 0, 1, 2, and 3 quantum units. An additional significant result is that as the wire diameter was increased the maximum value of metastable circulation observed also increased.