Cooling to heating transition in an optomechanical cavity

We experimentally study the phase space distribution (PSD) of a mechanical resonator that is simultaneously coupled to two electromagnetic cavities. The first one, operating in the microwave band, is employed for inducing either cooling or self-excited oscillation (SEO), whereas the second one, operating in the optical band, is used for displacement detection. A tomography technique is employed for extracting the PSD from the signal reflected by the optical cavity. We monitor the time evolution of the transitions from an optomechanically cooled state to a state of SEO. This transition is induced by abruptly switching the microwave driving frequency from the red-detuned region to the blue-detuned one. The experimental results are compared with theoretical predictions that are obtained by numerically integrating the Fokker-Planck equation. The feasibility of generating quantum superposition states in the system under study is briefly discussed.