My work focusses on maximising the phenomenological case for quantum sensor experiments to probe dark matter, gravitational waves and other new physics beyond the Standard Model. Particularly with respect to upcoming terrestrial long-baseline atom interferometer experiments including the AION collaboration of which I am a member. As part of this, my work considers new theory targets for these experiments such as spin-2 ultra-light dark matter candidates, and screened fifth-forces. I also work on the backgrounds that may limit searches for new physics from environmental noise such as seismic waves and atmospheric turbulence.