Ultra-high Q Acoustic Resonance in Superfluid 4He

TL;DR

This paper reports the measurement of extremely high acoustic quality factors in superfluid helium-4 resonators, revealing temperature-dependent dissipation mechanisms and potential for advanced quantum and gravitational wave experiments.

Contribution

The study demonstrates record-high Q factors in superfluid helium resonators and characterizes their temperature dependence, advancing understanding of dissipation in macroscopic quantum systems.

Findings

Q factors up to 1.4×10^8 observed

Q follows a T^{-4} temperature dependence

Dissipation attributed to dilute helium-3 impurities

Abstract

We report the measurement of the acoustic quality factor of a gram-scale, kilo-hertz frequency superfluid resonator, detected through the parametric coupling to a superconducting niobium microwave cavity. For temperature between 400mK and 50mK, we observe a $T^{-4}$ temperature dependence of the quality factor, consistent with a 3-phonon dissipation mechanism. We observe Q factors up to $1.4\cdot10^8$, consistent with the dissipation due to dilute $^3$He impurities, and expect that significant further improvements are possible. These experiments are relevant to exploring quantum behavior and decoherence of massive macroscopic objects, the laboratory detection of continuous wave gravitational waves from pulsars, and the probing of possible limits to physical length scales.