A micromechanical resonator to reach the quantum regime

We present a new micromechanical resonator designed for the observation of its quantum ground state (QGS). To reach QGS, a high frequency resonator with the lowest possible mass and the highest possible quality factor, coupled with an extremely sensitive measurement technique, has to be implemented. Using a high-finesse Fabry-Perot cavity with a mirror coated on the resonator, we expect benefits from the unique sensitivity of optical interferometry (10^-38 m²/Hz) and from the optomechanical coupling between the light and the micro-resonator both to laser cool the resonator down to its ground state and to observe its residual quantum position fluctuations. We present the resonator we have developed for that purpose, which takes advantage from the high intrinsic quality factor of single crystal quartz and is designed to obtain a high resonance frequency (a few MHz) as well as a low mass (a few tens of μg). A length extension mode is used in order to avoid any deformation of the mirror surface and so to preserve the intrinsic quality factor of the resonator. A dedicated crystallographic orientation and a beam equilateral cross section have been defined with respect to the quartz trigonal symmetry, allowing the micromachining of the resonator by wet etching. A beam cross-section area of 10^-2 mm² has been chosen to ease the deposit of the multilayered mirror. First mechanical characterizations of the resonator give a resonance frequency of 3.6 MHz, with a 25 μg mass and a quality factor of 390 000. Next steps will be the coating of the low-loss mirror on the resonator and its implementation in the Fabry-Perot cavity.