Phase slips and rotation detection

From early astronomical observations to the "state-of-the-art" Gravity Probe B experiment, increasingly sophisticated gyrometric mechanical devices have been used to monitor the rotation of the Earth. In addition, interferometric techniques exploiting the wave-mechanical nature of light beams — the Sagnac effect — have been devised in order both to demonstrate the general laws of inertia and to improve gyrometric techniques.

In a collaboration at Saclay, Paris, we have worked on an experiment [PRL78, 3602 (1997)] in which the effect of Earth rotation on a loop of superfluid ⁴He was measured with the help of quantum phase slippage. The principle of this experiment (see FIG.) is based on the possibility to measure with great accuracy the change in circulation of the superfluid velocity around a loop using a hydromechanical Helmholtz resonator. Detailed analysis of critical velocity distributions for phase slips in opposite directions was employed to measure the rotation velocity of the Earth to a resolution of better than 1%. This work gives a nice illustration of how phase coherence in the superfluid can be utilized to measure extremely small velocity circulations.

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