Superfluid Josephson Weak Links: Physics and Applications

Richard Packard, University of California, Berkeley

During the past few years arrays of nanometer sized apertures connecting reservoirs of superfluid helium have been found to exhibit properties described by the two Josephson equations. This talk will describe some of the experiments, in 3He below 1mK, and in 4He near 2K, which reveal the quantum nature of these weak links. Both of these superfluids exhibit Josephson oscillations, the so called “quantum whistle”. As temperature rises, 4He weak link arrays morph continuously from a phase slip regime into a Josephson sine-like current-phase relation. It is still a mystery why these arrays exhibit quantum coherence over thousands of apertures. Sensitive rotation sensors (gyroscopes), analogous to the superconducting dc-squid, have been demonstrated in both 3He and 4He. Since the 4He devices operate near 2K, a regime accessible to mechanical cryocoolers, these sensors may advance the state of the art for geodesy, navigation and matter wave interferometry in general.

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