High-sensitivity three-mode optomechanical transducer

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 CO2 laser thermal tuning. We demonstrate a displacement sensitivity of similar to 1 x 10(-17) m/root 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 similar to 2 x 10(-20) m/root Hz limited by the quantum shot noise is achievable with optimization of the cavity parameters.