Optical monitoring and cooling of a micro-mechanical oscillator to the quantum limit

Detecting quantum fluctuations of a mechanical resonator is a long-standing goal of experimental physics. Recent progress has been focussed on high frequency (MHz to GHz) resonators inserted in a milli-Kelvin environment, with motion detection performed by single electron transistor means. Here we propose a novel experimental approach based on high-sensitivity optical monitoring of the displacement of the resonator and feedback cooling. The experimental setup is based on a micro-mechanical resonator inserted in a high-finesse optical cavity and monitored by a highly-stabilized laser system. Available optical technologies provide an unequalled sensitivity, in the 10(-20) m/root Hz range. The displacement signal is used in real-time to perform a feedback cooling in order to set the resonator's fundamental mode of vibration in its quantum ground state. With the resonator at cryogenic temperature, the feedback cooling mechanism should allow to reach an effective temperature in the micro-Kelvin range.