Abstract: Superfluid helium-4 at millikelvin temperatures is an ideal acoustic medium, featuring ultralow dissipation and the unique possibility of tuning the mechanical frequency through pressurization. Combined with a cavity optomechanical readout to sensitively probe the motion, a superfluid resonant mass is a promising tabletop-scale platform to probe small mechanical signals and new physics, such as gravitational waves and dark matter. Previously, we demonstrated a prototype superfluid gravitational wave detector, setting the base for developing our Helium ultraLIght dark matter Optomechanical Sensor (HeLIOS). After reviewing superfluid optomechanical systems and motivating the detection of wavelike dark matter, I will present a recent characterization of our HeLIOS prototype. It promises unprecedented sensitivity and scalability to expand the search for dark matter, which nature is one of the biggest unsolved questions in modern science.
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