Superfluid helium quantum interference devices (SHeQUIDs): principles and performance

We describe recent progress in developing a superfluid helium analog of the superconducting dc-SQUID. The devices tested thus far are sensitive detectors of rotation as well as useful probes for studies of superfluidity. The key ingredients of the superfluid helium quantum interference device (SHeQUID) involve commercially available technology and modest cryogenic facilities. The superfluid states of quantum liquids (He-B and He) are described by a macroscopic order parameter of the form Ψ = ρs e iφ , where ρs is the superfluid density and φ is the quantum mechanical phase [1]. When two such fluids are coupled together through a small channel, the system exhibits many surprising features. Quintessential phenomena are various Josephson effects, which occur when the channel between the two fluids is sufficiently small. Such a small channel is normally referred to as a weak link or junction. In that scenario, solving the time-dependent Schrodinger’s equation applied to the coupled system results in two governing equations: I = I0 sinΔφ (1)