Direct detection of gravitational waves is opening a new window onto our universe. Here, we study the sensitivity to continuous-wave strain fields of a kg-scale optomechanical system formed by the acoustic motion of superfluid helium-4 parametrically coupled to a superconducting microwave cavity. This narrowband detection scheme can operate at very high Q-factors, while the resonant frequency is tunable through pressurization of the helium in the 0.1-1.5 kHz range. The detector can therefore be tuned to a variety of astrophysical sources and can remain sensitive to a particular source over a long period of time. For reasonable experimental parameters, we find that strain fields on the order of h∼10−23/Hz are detectable. We show that the proposed system can significantly improve the limits on gravitational wave strain from nearby pulsars within a few months of integration time.
@article{arxiv.1606.04980,
title = {Detecting continuous gravitational waves with superfluid $^4$He},
author = {S. Singh and L. A. De Lorenzo and I. Pikovski and K. C. Schwab},
journal= {arXiv preprint arXiv:1606.04980},
year = {2017}
}