Experiments with superfluid oscillators: Design and microfabrication of a superfluid gyroscope; modulation of a helium-4 rf SQUID analog by the earth's rotation; vortex nucleation in superfluid helium-4.

摘要

This thesis reports the results from experiments with superfluid {dollar}sp4{dollar}He Helmholtz oscillators. The purpose of these experiments are two fold: investigation of quantized dissipation in superfluid {dollar}sp4{dollar}He, and the construction of a device which relies on this quantized dissipation, to detect absolute rotation. Both of these topics represent unsolved problems which have existed for several decades in low temperature physics: the so called "critical velocity problem", and the realization of the superfluid {dollar}sp4{dollar}He analog of the superconducting rf SQUID.; The superfluid analog of the superconducting rf SQUID is a new device which is demonstrated in this thesis to be a sensitive gyroscope. A superfluid Helmholtz oscillator which displays behavior analogous to an rf SQUID is discussed and analyzed. Various oscillator designs and attempts to observe the rotational modulation of such a device are described, and culminates in a working design and successful observation of the modulation from the Earth's rotation.; This thesis also details the theory, calculation, and construction of these superfluid devices. Using various computer codes, it is shown how to calculate from first principles the rotational coupling of a superfluid gyroscope, and the effect of stochastic vortex nucleation on the measured staircase response. This work includes the development of microfabrication techniques which demonstrate a novel technique to construct minimum volume, high rotational coupling, superfluid devices.; The experiments here, relevant to the "critical velocity problem," try to answer the question: "How do the vortices, which are responsible for dissipation in superfluid {dollar}sp4{dollar}He flow in small apertures, come into existence?" These experiments provide further evidence that the dissipation in superfluid {dollar}sp4{dollar}He is a result of the motion of quantized vortices and that these vortices are thermally nucleated over a universal energy barrier. We also discovered a new phenomenon in which dissipation-free flow contains a "memory" of previous phase slips.