Coherent Feedback Cooling of a Nanomechanical Membrane with Atomic Spins
Coherent feedback stabilises a system towards a target state without the need of a measurement, thus avoiding the quantum backaction inherent to measurements. In our experiment, we employ optical coherent feedback to remotely cool a nanomechanical membrane oscillator using the collective spin of an atomic ensemble as controller. Direct time-controlled manipulation of the spins allows us to tune the spin-membrane interaction from strong coupling to an overdamped regime. By applying a stroboscopic cooling, the cooling rate can be increased by a factor of two such that we can cool the membrane in a room-temperature environment to 216 mK (2.3x103 phonons) in 200 µs. See our paper in PRX or read more in the Physics Viewpoint.