Prototype Superfluid Gravitational Wave Detector

TL;DR

This paper presents a prototype superfluid helium-based resonant gravitational wave detector with high sensitivity and tunable frequencies, capable of detecting continuous gravitational waves in the 1-30 kHz range.

Contribution

It introduces a novel superfluid helium resonant-mass detector with optomechanical transduction and tunable frequencies for broadband gravitational wave detection.

Findings

Achieved strain sensitivity of 8×10⁻¹⁹ Hz⁻¹/² at 20 mK

Observed thermally excited high-Q acoustic modes of helium

Demonstrated frequency tuning up to 173 Hz/bar

Abstract

We study a cross-shaped cavity filled with superfluid $^4$He as a prototype resonant-mass gravitational wave detector. Using a membrane and a re-entrant microwave cavity as a sensitive optomechanical transducer, we were able to observe the thermally excited high-$Q$ acoustic modes of the helium at 20 mK temperature and achieved a strain sensitivity of $8 \times 10^{-19}$ Hz$^{-1/2}$ to gravitational waves. To facilitate the broadband detection of continuous gravitational waves, we tune the kilohertz-scale mechanical resonance frequencies up to 173 Hz/bar by pressurizing the helium. With reasonable improvements, this architecture will enable the search for GWs in the 1-30 kHz range, relevant for a number of astrophysical sources both within and beyond the Standard Model.