A path to combining squeezing and quantum non-demolition techniques to improve the prospects for the gravitational direct detection of dark matter

Optomechanical systems have enabled a variety of novel sensors that transduce a force to a quantum-limited signal. Recent advances in these sensing technologies have led to the suggestion that heavy dark matter candidates around the Planck mass range could be detected solely through their gravitational interaction. The Windchime collaboration is developing the necessary techniques, systems, and experimental apparatus using arrays of optomechanical sensors that operate in the regime of high-bandwidth force detection, i.e., impulse metrology. Today's state-of-the-art sensors can be limited by the added noise due to the act of measurement itself. Techniques to go beyond this limit include both squeezing of the light used for measurement and incorporating backaction evading measurement by estimating quantum non-demolition operators — typically the momentum of a mechanical resonator well above its resonance frequency. Here we explore the theoretical limits to noise reduction while combining these two quantum enhanced readout techniques for these optomechanical sensors. We find that backaction evasion via velocity sensing not only works with squeezing, but it also dramatically reduces the technical challenges of using squeezed light for broadband force detection, paving the way for combining two different quantum noise reduction techniques in the context of impulse metrology.