Progress on the Detection of Single Free Helium Atoms through Field Ionization for a Dark Matter Detector

We describe recent progress on the detection of free helium atoms by field ionization,
which is a key element of a new liquid helium-based method of dark matter detection
proposed by Maris, Seidel and Stein [1]. When a dark matter particle collides with a
liquid He atom it produces phonons and rotons which propagate through the superfluid,
eventually arriving at the surface. These excitations can then evaporate a He atom,
which can then be detected through field ionization, the process of ionizing them in a
strong electric field using sharp, metal nanotips. The ability of field ionization to detect
even a single helium atom, combined with the < 1 meV binding energy of a He atom to
the superfluid surface, could potentially allow for the detection of dark matter particles
with masses down to 1 MeV/c².