Hybrid Quantum Sensing of Phonons for Dark Matter Detection

Dark matter can be inferred through its gravitational interaction, but we currently know little more about it besides that its other interactions with conventional matter are weak. There is a concerted effort to develop detectors for low-mass dark matter, which deposit small amounts of energy. Detectors with meV energy resolution (phonons) would allow one to reach the keV-mass warm dark matter limit, accessing some of the most interesting benchmark dark matter models, and extending the reach to athermal dark matter by three orders of magnitude beyond electronic excitation. However, efficient detection of phonons with negligible background is difficult – 1 kg of an ionic crystal with a 1 meV energy threshold is estimated to have of order one such dark matter event per minute. Here we will discuss a new detector concept which promises to detect 1 meV phonons based on quantum sensing of the spin of quantum-evaporated ³He atoms. We show that ³He atoms can be localized under an electron bound to the helium surface through the local reduction of the surface tension. The nuclear spin of the collected and localized ³He can decohere an electron's spin in a quantum dot-type device. Structures to measure the spin of single electrons bound to a helium surface are under active investigation.