Prototype superfluid gravitational wave detector

Abstract

We study a cross-shaped cavity filled with superfluid as a prototype resonant-mass gravitational wave detector. Using a membrane and a reentrant microwave cavity as a sensitive optomechanical transducer, we were able to observe the thermally excited high- acoustic modes of the helium at 20 mK temperature and achieved a strain sensitivity of to gravitational waves. To facilitate the broadband detection of continuous gravitational waves, we tune the kilohertz-scale mechanical resonance frequencies up to by pressurizing the helium. With reasonable improvements, this architecture will enable the search for gravitational waves in the range, relevant for a number of astrophysical sources both within and beyond the Standard Model.