Ground-state cooling of a mechanical resonator enabled by critical coupling and dark entangled states

Over the past ten years, there has been tremendous interest in achieving ground-state cooling in mechanical resonators in order to enhance the performance characteristics of mechanical-based sensors, quantum memories, and quantum transducers. While there have been successful demonstrations of ground-state cooling using optomechanical systems, an outstanding challenge remains in reaching the ground state using solid-state defects. In this work, we present a novel approach for resonant phonon cooling using the concept of critical coupling, subradiance, and many-body entanglement within an ensemble of two-level systems. We reveal that carefully engineering the strain profile of the mechanical resonator allows phonon cooling to proceed through the dark entangled states of an interacting ensemble, thereby enabling ground-state cooling in spite of the small spin-strain coupling strengths encountered in real systems. Our work provides a new avenue for phonon cooling and should be accessible for experimental demonstrations.