Superfluid Optomechanics: Coupling of a Superfluid to a Superconducting Condensate

TL;DR

This paper explores a superfluid optomechanical system coupling superfluid helium with a superconducting resonator, achieving high-quality acoustic modes and potential applications in quantum sensing and fundamental physics studies.

Contribution

It demonstrates the coupling of superfluid helium to a superconducting resonator with record-high quality factors, advancing the development of macroscopic quantum systems.

Findings

Achieved acoustic mode quality factors up to 7 million.

Identified intrinsic three phonon processes as dissipation at higher temperatures.

Projected quality factors approaching 10^11 in isotopically purified samples at millikelvin temperatures.

Abstract

We investigate the low loss acoustic motion of superfluid $^4$He parametrically coupled to a very low loss, superconducting Nb, TE$_{011}$ microwave resonator, forming a gram-scale, sideband resolved, optomechanical system. We demonstrate the detection of a series of acoustic modes with quality factors as high as $7\cdot 10^6$. At higher temperatures, the lowest dissipation modes are limited by an intrinsic three phonon process. Acoustic quality factors approaching $10^{11}$ may be possible in isotopically purified samples at temperatures below 10 mK. A system of this type may be utilized to study macroscopic quantized motion and as an ultra-sensitive sensor of extremely weak displacements and forces, such as continuous gravity wave sources.