Direct measurement of the current-phase relation of a superfluid He-3-B weak link

Direct measurements of the current-phase relation, I versus Delta phi, for a weak link coupling two reservoirs of B-phase superfluid helium-3 (He-3-B) were made over a wide range of temperatures. The weak link consists of a square array of 100-nanometer-diameter apertures. For temperatures T such that T/T-c greater than or equal to 0.6 (where T-c is the superfluid transition temperature), I proportional to sin(Delta phi). At lower temperatures, (Delta phi) approaches a straight line. Several remarkable phenomena heretofore inaccessible to superconducting Josephson junctions, including direct observation of quantum oscillations and continuous knowledge of Delta phi, were also observed.