Observation of strong radiation pressure forces from squeezed light on a mechanical oscillator

In quantum-enhanced sensing, non-classical states are used to improve the sensitivity of a measurement(1). Squeezed light, in particular, has proved a useful resource in enhanced mechanical displacement sensing(2-8), although the fundamental limit to this enhancement due to the Heisenberg uncertainty principle(9-11) has not been encountered experimentally. Here we use a microwave cavity optomechanical system to observe the squeezing-dependent radiation pressure noise that necessarily accompanies any quantum enhancement of the measurement precision and ultimately limits the measurement noise performance. By increasing the measurement strength so that radiation pressure forces dominate the thermal motion of the mechanical oscillator, we exploit the optomechanical interaction to implement an efficient quantum nondemolition measurement of the squeezed light(12). Thus, our results show how the mechanical oscillator improves the measurement of non-classical light, just as non-classical light enhances the measurement of the motion.