Development of a Planar Josephson Junction for Helium-4

We are investigating the transport of superfluid helium-4 through a two dimensional, nano-porous polymer material in the temperature interval 300mK to {\$}T\textunderscore $\backslash $lambda{\$}. The crystalline material is covalently bonded, a single molecule thick, and supported on a 50nm silicon nitride frame, covering a two-micron aperture. We expect this junction structure to realize a weak-link for temperatures far below the superfluid transition temperature, leading to much larger critical current densities than previously demonstrated junctions which operate very close to {\$}T\textunderscore $\backslash $lambda{\$} where the superfluid density and resulting mass current is greatly reduced. We expect this junction to lead to ultra-sensitive superfluid interferometers with the sensitivity beyond that of atomic matter wave interferometers and the sensitivity to resolve the fluctuations in the Earth rotation in a hand-sized device.