Near-field cavity optomechanics with nanomechanical oscillators

Abstract

Cavity-enhanced radiation pressure coupling between photons and mechanical degrees of freedom gives rise to dynamical backaction enabling both amplification and cooling of mechanical motion. Moreover, this optomechanical coupling allows quantum-limited position measurements. Despite recent proposals and experiments, however, these distinguishing features of cavity optomechanics have been limited to micro- and macro-scale mechanical oscillators, owing to the size disparity of nanoscale objects with the diffraction limit imposed on propagating fields. Here we demonstrate cavity optomechanics at the nanoscale by dispersively coupling high quality nanomechanical oscillators to ultra-high finesse optical microresonators via evanescent fields. Dynamical backaction mediated by the optical dipole force is observed and salient features such as laser-like amplification of mechanical motion are reported. Moreover, we achieve sub-fm/Hz^(1/2) displacement sensitivity (at room temperature), exceeding the sensitivity of position detectors based on electron flow and allowing access to quantum-limited readout of nanomechanical motion. The reported near-field approach provides a versatile platform to which diverse oscillators, such as nanowires, graphene sheets or carbon nanotubes can be tunably coupled, extending cavity optomechanics into the realm of nanomechanical oscillators. This could have wide implications for probing quantum phenomena of mechanical systems and equally in precision experiments that are based on ultra-sensitive nanomechanical oscillators. The combination of picogram, high quality factor nanostrings with ultra-high finesse microresonators moreover provides a route to quantum optomechanical experiments at room temperature.