Nonlinear cavity optomechanics with nanomechanical thermal fluctuations

In optomechanical systems, co-localizing light and mechanical oscillations at the nanoscale can lead to strong interaction between photons and phonons. Such optomechanical coupling enables sensitive detection of nanoscale motion, as well as control of the motion through optical forces down to the quantum level [1]. In the vast majority of cases, the optomechanical coupling can be regarded as linear. In this work, we exploit subwavelength optical field confinement to realize record-high interaction strengths, such that thermal motion induces optical frequency fluctuations larger than the intrinsic optical linewidth. The system thereby operates in a new — fully nonlinear — regime, which pronouncedly impacts optical response, displacement measurement, and radiation pressure effects [2]. We explore those implications, and demonstrate that the strong nonlinearity could be used for novel ways to measure and control mechanical quantum states.