Low-Loss Optomechanical Oscillator for Quantum-Optics Experiments

We present an oscillating micromirror with mechanical quality factors Q up to 1.2 × 106 at cryogenic temperature and optical losses lower than 20 ppm. The device is specifically designed to ease the detection of ponderomotive squeezing (or, more generally, to produce a cavity quantum optomechanical system) at frequencies of about 100 kHz. The design allows one to keep under control both the structural loss in the optical coating and the mechanical energy leakage through the support. The comparison between devices with different shapes shows that the residual mechanical loss at 4.2 K is equally contributed by the intrinsic loss of the silicon substrate and of the coating, while at higher temperatures the dominant loss mechanism is thermoelasticity in the substrate. As the modal response of the device is tailored for its use in optical cavities, these features make the device very promising for quantum-optics experiments.