Cooling of mechanical motion with a two-level system: The high-temperature regime

We analyze cooling of a nanomechanical resonator coupled to a dissipative solid-state two-level system focusing on the regime of high initial temperatures. We derive an effective Fokker-Planck equation for the mechanical mode which accounts for saturation and other nonlinear effects and allows us to study the cooling dynamics of the resonator mode for arbitrary occupation numbers. We find a degrading of the cooling rates and eventually a breakdown of cooling at very high initial temperatures and discuss the dependence of these effects on various system parameters. Our results apply to most solid-state systems which have been proposed for cooling a mechanical resonator including quantum dots, superconducting qubits, and electronic spin qubits.