Mechanical resonators in the middle of an optical cavity

The interaction of light with mechanical motion has generated a burst of interest in recent years [1–4] from fundamental questions on the quantum motion of solid objects to novel engineering concepts for sensing and optical devices. This interest was originally inspired by experimental geometries in which a mechanically compliant object acts as the back mirror of Fabry-Perot cavity. In order to maintain a stable, high-finesse cavity with this geometry, the mechanical element’s transverse dimensions must be larger than the photon’s wavelength and its thickness sufficient to create an appreciable reflectivity. This places a lower bound on the mass of the mechanical object, limiting the effect of individual photons. Here we explore a complementary set of geometries in which a nanomechanical element or a very thin membrane is positioned within a high-finesse, rigid optical cavity. This geometry (inspired by the success of cavity quantum electrodynamics experiments with atoms) extends Fabry-Perot-based optomechanics to smaller / sub-wavelength mechanical elements. The added complexity associated with inserting a third (movable) scatterer also affords a new set of opportunities: in addition to reproducing the physics of a two-mirror optomechanical system, several “non-standard” types of linear and non-linear optomechanical couples can be generated. Combined with the diverse set of comparatively lightweight mechanical elements that can be inserted into a cavity, this geometry offers a high degree of optomechanical versatility for potential sensing and quantum information applications.