The Superfluid Helium Ultralight Dark Matter Detector HeLIOS

The absence of a breakthrough in directly observing dark matter (DM) motivates the development of novel tabletop experiments probing more exotic regions of the parameter space. If DM contains bosonic particles lighter than ∼10 eV/c², they would behave as a classical wave and could manifest through an oscillating force on baryonic matter that is coherent over ∼10⁶ periods^1,2. Our Helium ultraLIght dark matter Optomechanical Sensor (HeLIOS) uses the low-loss acoustic modes of superfluid helium-4 to resonantly amplify this signal at millikelvin temperatures. Pressurizing the helium allows for the unique possibility of tuning the mechanical frequency to effectively broaden the DM detection bandwidth. Building upon our recent HeLIOS prototype³, we are now developing an improved detector, aiming for a stronger DM coupling while reducing mechanical and readout noise. We show that the next HeLIOS generation could already explore unconstrained parameter space of both scalar and vector ultralight DM between 1 and 100 peV/c² after just an hour of integration time.

[1] PRL 116, 031102 (2016). [2] PRA 97, 042506 (2018). [3] PRD 109, 095011 (2024).