Superfluid Helium-4 Weak Link Experiments with Nanoscale Aperture Arrays

Arrays of nanoscale apertures on thin (~ 60 nm) silicon nitride membranes have been discovered to exhibit the characteristic signatures of so-called Josephson weak links in superfluid helium-4 (4He) [1]. These devices can be used to detect quantum phase differences in a matter wave interferometer made with two weak-links in a loop [2]. We summarize here our recent [3] observation of quantum interference (the characteristic pattern predicted for 4-slit optical interference) from a 4He grating structure consisting of four weak links. We also report here a new displacement sensor [4] that uses a rare-earth magnet attached to a flexible diaphragm for use in our superfluid experiments with the nanoscale aperture arrays. Some fabrication issues and outstanding questions are discussed [8]. Summary of Research: