Interferometric measurements of the position of a macroscopic body: Towards observation of quantum limits

An optomechanical sensor suitable for the study of quantum effects has been developed and characterized. The sensor reads out the vibrations of a microfabricated miniature silicon mechanical oscillator which forms one end mirror of a high finesse Fabry-Pérot cavity. The mechanical quality factor is up to $Q=300\mathrm{}000$ at 300 K and rises up to $Q=4\mathrm{}\times {10}^6$ at 4 K. The thermal noise of the oscillator has been measured in the time and frequency domains at room temperature and at 4.5 K. The prospects for observing the standard quantum limit are discussed.