Prototype superfluid gravitational wave detector
Vaisakh Vadakkumbatt, M. Hirschel, Jack Manley, Thomas J. Clark, Swati Singh, J. P. Davis
Abstract
We study a cross-shaped cavity filled with superfluid $^{4}\mathrm{He}$ 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-$Q$ acoustic modes of the helium at 20 mK temperature and achieved a strain sensitivity of $8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\text{ }\text{ }{\mathrm{Hz}}^{\ensuremath{-}1/2}$ to gravitational waves. To facilitate the broadband detection of continuous gravitational waves, we tune the kilohertz-scale mechanical resonance frequencies up to $173\text{ }\text{ }\mathrm{Hz}/\mathrm{bar}$ by pressurizing the helium. With reasonable improvements, this architecture will enable the search for gravitational waves in the $1--30\text{ }\text{ }\mathrm{kHz}$ range, relevant for a number of astrophysical sources both within and beyond the Standard Model.