Detecting continuous gravitational waves with a jug of superfluid

We investigate the sensitivity to narrow band, continuous-wave strain fields of a kg-scale optomechanical system formed by the acoustic motion of superfluid helium-4 parametrically coupled to a super-conducting microwave cavity. This narrowband detection scheme is tunable through pressurization of the helium, thereby making both doppler tracking of astrophysical sources and tuning the detector on/off from the source possible. For reasonable experimental parameters, we find that gravitational metric strain fields from nearby pulsars could be detected with a few weeks of integration time.