Jeudi 16 avril 1996
In this lecture I will describe recent experiments with superfluid helium which although they involve complex hydrodynamic processes, yield simple results based on the Josephson-Anderson equation. In one experiment a quantized vortex filament is discovered to precess at a frequency which is easily calculated using the above equation. This experiment represents a direct verification of the so called Josephson-Anderson frequency relation.
In a second experiment the Josephson-Anderson equation is found to=20 correctly predict that superfluid flow energy is dissipated in discrete units (2 pi phase slips) whose magnitude is determined by the flow geometry. The equation also permits one to deduce the shape of the energy barrier for the nucleation of quantized vortex lines. This second type of experiment has opened the possibility to develop a very sensitive detector of absolute rotation, the superfluid analog of the superconducting SQUID.
Since these experiments use techniques at temperatures as low as 160 microK, the talk will provide some flavor of the state-of-the-art in submillikelvin superfluid probes.