  We propose a method to identify the direction of an incident Weakly
Interacting Massive Particle (WIMP) via induced nuclear recoil. Our method is
based on spectroscopic interrogation of quantum defects in macroscopic
solid-state crystals . When a WIMP scatters in a crystal, the induced nuclear
recoil creates a tell-tale damage cluster, localized to within about 50 nm,
with an orientation to the damage trail that correlates well with the direction
of the recoil and hence the incoming WIMP. This damage cluster induces strain
in the crystal, shifting the energy levels of nearby quantum defects. These
level shifts can be measured optically (or through paramagnetic resonance)
making it possible to detect the strain environment around the defect in a
solid sample. As a specific example, we consider nitrogen vacancy centers in
diamond, for which high defect densities and nanoscale localization of
individual defects have been demonstrated. To localize the millimeter-scale
region of a nuclear recoil within the crystal due to a potential dark matter
event, we can use conventional WIMP detection techniques such as the collection
of ionization/scintillation. Once an event is identified, the quantum defects
in the vicinity of the event can be interrogated to map the strain environment,
thus determining the direction of the recoil. In principle, this approach
should be able to identify the recoil direction with an efficiency greater than
70% at a false positive rate less than 5% for 10 keV recoil energies. If
successful, this method would allow for directional detection of WIMP-induced
nuclear recoils at solid state densities, enabling probes of WIMP parameter
space below the solar neutrino floor. This technique could also potentially be
applied to identify the direction of particles such as neutrons whose low
scattering cross-section requires detectors with a large target mass.

High Energy Physics - Phenomenology;Quantum Physics