SGER: Response of Suspended Helium Films to Pulsed Atomic Helium Beams

9980329

Halley

This is an SGER project that addresses a fundamental issue in the physics of superfluid helium. The experiments are designed to test predictions that effects of long range quantum coherence in the fluid will lead to some very rapid transmission events, not associated with the time for sound propagation across the superfluid. Pulsed atomic beams of helium atoms impinge on a suspended film of superfluid helium. The experiments will measure delay times for helium atoms transmitted through the film. Transmission at two different delay times is predicted: the longer delay time is associate with production by the incident atoms of excitation of the phonon-roton spectrum of the fluid, followed by reemission of atoms from the surface. A second, shorter, delay time is predicted to arise from the momentary virtual displacement of the entire superfluid as a result of interaction with an incident atom, followed by reemission. This event is extremely fast, probably in the picosecond range. Only the longer delay (estimated at microseconds) transmission will be detected. The amplitude of the shorter delay transmission can be determined from the time delay information and knowledge of the initial flux. The results will be of fundamental interest in connection with the coherent character of the helium atoms in Bose-condensate-like state of superfluid helium. The experiments provide exciting educational opportunities for students to be involved in fundamental research using state-of-the-art research tools.

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This is an SGER project that addresses a fundamental issue in the physics of superfluid helium. The project seeks to detect the 'coherent' state of superfluid in which all the helium atoms in the superfluid respond as a unit. The procedure will be to 'shoot' helium atoms off into a suspended vertical film of helium maintained near absolute zero. Some of the incident helium atoms will rapidly bounce off the coherent state of superfluid helium, some will interact with helium atoms and be delayed. The experiments seek to test theoretical predictions for these two events. The results are of fundamental importance for the general field of 'Bose-Einstein condensates', which includes Bose condensates in the atomic gas state. The experiments provide exciting educational opportunities for students who are involved in fundamental research using state-of-the-art research tools.