High-sensitivity optical monitoring of a micro-mechanical resonator with   a quantum-limited optomechanical sensor
  We experimentally demonstrate the high-sensitivity optical monitoring of a micro-mechanical resonator and its cooling by active control. Coating a low-loss mirror upon the resonator, we have built an optomechanical sensor based on a very high-finesse cavity (30000). We have measured the thermal noise of the resonator with a quantum-limited sensitivity at the 10^-19 m/rootHz level, and cooled the resonator down to 5K by a cold-damping technique. Applications of our setup range from quantum optics experiments to the experimental demonstration of the quantum ground state of a macroscopic mechanical resonator. 
O. Arcizet, P.-F. Cohadon, T. Briant, M. Pinard, A. Heidmann, J.-M.   Mackowski, C. Michel, L. Pinard, O. Francais, L. Rousseau