We study a cross-shaped cavity filled with superfluid 4He 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 8×10−19 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.
@article{arxiv.2107.00120,
title = {Prototype Superfluid Gravitational Wave Detector},
author = {V. Vadakkumbatt and M. Hirschel and J. Manley and T. J. Clark and S. Singh and J. P. Davis},
journal= {arXiv preprint arXiv:2107.00120},
year = {2025}
}