I will describe a novel sensor technology, in which meV-scale excitations of superfluid 4He are read out using 'quantum evaporation' of 4He atoms into the vacuum above. We are motivated by the possibility that dark matter may be hiding at low (keV-MeV) mass scales, lighter than the standard WIMP hypothesis. At these lower masses, the recoil endpoint energy will be in the meV-eV range, and the single dominating technological challenge becomes sensor threshold. Superfluid 4He offers unique pathways for pushing threshold into this sub-eV regime, and testing otherwise untestable dark matter models.
