High-sensitivity three-mode optomechanical transducer

Abstract

Three-mode optomechanical interactions have been predicted to allow the creation of very high sensitivity transducers in which very strong optical self-cooling and strong optomechanical quantum entanglement are predicted. Strong coupling is achieved by engineering a transducer in which both the pump laser and a single signal sideband frequency are resonantly enhanced. Here we demonstrate that very high sensitivity can be achieved in a very simple system consisting of a Fabry-Perot cavity with CO${}_{2}$ laser thermal tuning. We demonstrate a displacement sensitivity of $\ensuremath{\sim}$$1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}\phantom{\rule{0.28em}{0ex}}\text{m}/\sqrt{\text{Hz}}$, which is sufficient to observe a thermally excited acoustic mode in a 5.6 kg sapphire mirror with a signal-to-noise ratio of more than 20 dB. It is shown that a measurement sensitivity of $\ensuremath{\sim}$$2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}\phantom{\rule{0.28em}{0ex}}\mathrm{m}/\sqrt{\mathrm{Hz}}$ limited by the quantum shot noise is achievable with optimization of the cavity parameters.