Cooling a Mechanical Resonator with a Nitrogen-Vacancy Center Ensemble Using a Room Temperature Excited State Spin-Strain Interaction*

Cooling a mechanical resonator mode to a sub-thermal state has been a long-standing challenge in physics. This pursuit has recently found traction in the field of optomechanics in which a mechanical mode is coupled to an optical cavity. An alternate method is to couple the resonator to a well-controlled two-level system. We propose a protocol to dissipatively cool a room temperature mechanical mode using a nitrogen-vacancy (NV) center spin ensemble. The ensemble is coupled to the resonator through a spin-strain interaction in its orbitally-averaged excited state that is $13.5\pm0.5$ times stronger than the ground state NV center spin-strain coupling. This interaction, combined with a high-density spin ensemble, enables the cooling of a mechanical resonator from room temperature to a fraction of its thermal phonon occupancy.