Cooling of macroscopic mechanical resonators in hybrid atom-optomechanical systems

Cooling macroscopic objects is of importance for both fundamental and applied physics. Here we study the optomechanical cooling in a hybrid system which consists of a cloud of atoms coupled to a cavity optomechanical system. On one hand, the asymmetric Fano or electromagnetically induced transparency resonance is explored and the steady-state cooling limits of resonators with frequency ωₘ are analytically obtained, permitting ground-state cooling of massive low-frequency resonators beyond the resolved sideband limit. On the other hand, due to the excitation-saturation effect, the validity of cooling requires the number of atoms to be much larger than the number of steady-state excitations, which is proportional to ωₘ^-2. Thus, this limitation plays a minor role in cooling higher-frequency resonators, but becomes important for macroscopic lower-frequency resonators. Under such limitation on the number of atoms, the optimal parameters are quantified. Our study can be a guideline for both theoretical and experimental study of cooling macroscopic objects in atom-optomechanical hybrid systems.