Superfluid weak links; physics and applications

Superfluid helium is an “entangled” Bose condensed state of matter in which the individual atoms relinquish their identity to share in a macroscopic wavefunction whose quantum phase depends on external fields. The key element required to measure the quantum phase information is an array of nanometer sized apertures that exhibit properties described by Josephson’s equations. We have studied these so-called superfluid weak links in both superfluid ³He and ⁴He. A remarkable observation is that when we try to push the superfluid through the apertures the fluid oscillates at a quantum frequency rather than flowing down the pressure gradient. By exploiting the weak link properties we have developed Superfluid Helium Quantum Interference Devices (SHeQUIDs) which are analogs of superconducting SQUIDs. These novel devices reveal the absolute rotation state of the walls confining the liquid and may find uses in geodesy and inertial navigation. Other SHeQUIDs may detect Aharonov-Bohm phase shifts in neutral nonpolar matter and may set upper limits to gravito-magnetic fields present near rotating masses. This talk will be understandable at the undergraduate level. For related papers and further discussion visit: http://www.physics.berkeley.edu/research/packard/