Detecting continuous gravitational waves with superfluid $^4$He

TL;DR

This paper proposes a superfluid helium-4 based optomechanical detector for continuous gravitational waves, capable of high sensitivity and tunability, potentially improving detection limits for nearby pulsars.

Contribution

It introduces a novel, tunable, high-Q resonant detection scheme using superfluid helium-4 coupled with microwave cavities for gravitational wave detection.

Findings

Detects strain fields around 10^{-23}/√Hz

Can tune to various astrophysical sources

Improves limits on pulsar gravitational waves

Abstract

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 $h\sim 10^{-23} /\sqrt{\rm Hz}$ 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.