Remote Cooling of Spin-ensembles Coupled to a Spin-mechanical Hybrid Interface

We present here a protocol for the ground-state cooling of a hybrid quantum system consisting of a spin ensemble, an oscillator, and a single probe spin. In the weak dispersive coupling limit between the spins and the oscillator, a back-action effect from frequent measurements of the probe spin allows exponential cooling of the hybrid system. We identify the parameter regimes necessary to cool the ensemble, the oscillator, or both to their thermal ground states. Our results contribute to the development of a practical solution for cooling/polarizing large spin ensembles. More importantly, we show that even with weak coupling, significant changes in the dynamics of such ensemble-oscillator hybrid systems can be achieved by manipulating a single spin. This result provides a relatively simple means of tuning the dynamics of a hybrid system, which might facilitate advances in many quantum technology applications such as preparing entangled states in macroscopic objects.