Optical Coherent Feedback Control of a Mechanical Oscillator

Feedback is a powerful and ubiquitous technique both in classical quantum system control. Its standard implementation relies on measuring the state of system, processing signal, feeding it back to system. In physics, however, measurements not only read out but also modify irreversibly. Coherent feedback different kind that coherently processes feeds signals without actually Here, we report experimental realization theoretical analysis an optical coherent platform control motional nanomechanical membrane cavity. The loop consists light field interacting twice with same mechanical mode through cavity modes, {performing any} measurement. Tuning phase delay allows us oscillator, its resonance frequency damping rate, which use cool close ground state. Our provides optimal cooling conditions, showing this new enables ground-state cooling. Experimentally, show can $\bar{n}_m = 4.89 \pm 0.14 $ phonons (${480}\,{\mu \mathrm{K}}$) ${20}\,\mathrm{K}$ environment. This lies below limit dynamical backaction unresolved sideband regime achieved 1$\%$ power required for scheme very versatile, offering opportunities variety optomechanical systems.