Feedback cooling of a trampoline in a high-finesse cavity from room temperature

The creation of macroscopic quantum systems represents a long-pursued goal for the quantum-technology community as it might shed new light on the theory of quantum mechanics and find application in quantum information science. Feedback cooling provides an efficient strategy to such objective, as it enables motion control of massive objects coupled to a light field. Several successful approaches have been developed to achieve cooling into the ground state. The system we present consists of a SiN tethered membrane (trampoline) placed inside an optical cavity with a finesse of 15000. The mechanical motion at 132 kHz is imprinted into the phase of a probing laser beam at 1550 nm and then readout by homodyne detection. The measurement results are then used to modulate the amplitude of a cooling beam which steers the trampoline towards the ground state via radiation pressure force. Figure 1c shows the results obtained in our feedback cooling scheme, which allowed to reach a final phonon number occupancy of 4000 starting from room temperature.