Quantum Fluids Research

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9807761 Packard This is low temperature physics project focusing on the properties of superfluid flowing through arrays of 100nm apertures. The work is based on the recent finding that such an array behaves as a Josephson weak link. A main part of the project will investigate the physics associated with the various Josephson effects in such arrays. The experiments will: (1) Map out the current-phase relation as a function of temperature and ambient pressure, (2) Determine the stability of metastable states of non-zero quantum phase difference, (3) Determine the stability of metastable state of non-zero quantum phase difference, (4) Look for phase mixing effects analogous to the superconducting Shapiro effect, (5) Determine the dissipative mechanism which exist a non-zero pressure head, and (6) Determine the effect of flux trapping and textural structures within and near the aperture array. The second part of the project will focus on detecting acoustic radiation associated with the phase slippage when He-4 passes through a submicron size aperture. Techniques to detect the acoustic radiation will be developed. Subsequently, the acoustic spectrum will be studied to learn about vortex nucleation mechanisms and the Josephson frequency relation. The project provides excellent training for graduate students in both fundamental and experimental physics. %%% This is a low temperature physics project that focuses on understanding the dynamic behavior of superfluids that pass through very small apertures. In the case of superfluid He-3, an aperture smaller than 1/10,000,000 meter forms a so-called quantum weak link. When the superfluid is forced through such a small aperture, instead of flowing in one direction like an ordinary liquid, the fluid surges back and forth at a frequency proportional to the force on the liquid. These Josephson oscillations indicate a sine-like relation ship between fluid current and quantum mechanical phase difference. The planned research will expand our understanding of the consequences of this relation. In the case of superfluid He-4, theory suggests that pressure driven flow through an aperture should be accompanied by a sound signal at the so-called Josephson frequency. The sound spectrum will reflect the detail of vortex nucleation within the aperture. The relation between the sound spectrum and the applied pressure head may lead to a quantum mechanical pressure standard. The project provides excellent training for graduate students in both fundamental and experimental physics. ***