Scheme for a quantum-limited force measurement with an optomechanical device

We study the detection of weak coherent forces by means of an optomechanical device formed by a highly reflecting isolated mirror shined by an intense quasimonochromatic laser beam. Radiation pressure excites a vibrational mode of the mirror, inducing sidebands of the incident field, which are then measured by heterodyne detection. We show that the sensitivity of such a scheme can surpass the standard quantum limit. In particular the use of an entangled input state of the two sideband modes improves the detection, even in the presence of damping and noise acting on the mechanical mode