Optical Coherent Feedback Control of a Mechanical Oscillator

Coherent Feedback Control

Coherent feedback is a kind of feedback that processes and feeds back quantum signals without measuring the system. We implemented a coherent feedback loop consisting of a light field interacting twice with the same mechanical mode of a membrane oscilator through different cavity modes, without performing any measurement. Tuning the optical phase and delay of the loop allows us to control the motional state of the oscillator, its resonance frequency, and its damping rate, which we use to cool the membrane close to the quantum ground state. A theoretical analysis also provides the optimal cooling conditions, showing that this new technique enables ground-state cooling. These results have been published in PRX.