A hybrid on-chip optonanomechanical transducer for ultra-sensitive force measurements

E. Gavartin, P. Verlot, T. J. Kippenberg

EPF Lausanne

Nanomechanical oscillators serve as ultrasensitive detectors of force, mass and charge. They are also used in opto- or electromechanical experiments with the goal of quantum control of mechanical systems. Here, we report the realization and operation of a hybrid monolithically integrated transducer system having a high force sensitivity of 74 aN Hz-1/2 at room temperature. Our system is particularly suited for the detection of small incoherent forces, which generally suffers from slow convergence with the fourth root of the averaging time. Using dissipative feedback  based on radiation pressure enabled control, we explicitly demonstrate by detecting a weak incoherent force that this constraint can be significantly relaxed. We achieve a more than 30-fold reduction in averaging time with our hybrid transducer and are able to detect an incoherent force having a force spectral density as small as 15 aN Hz-1/2 within 35 s of averaging. This corresponds to a signal, which is 25 times smaller than the thermal noise and would otherwise remain out of reach. The reported monolithic platform is thus an enabling step towards hybrid nanomechanical transducers relying on the light-mechanics interface.