Although the interaction between light and motion in cavity optomechanical systems is inherently nonlinear, experimental demonstrations to date have allowed a linearized description in all except highly driven cases. Here, we demonstrate a nanoscale optomechanical system in which the interaction between light and motion is so large (single-photon cooperativity C-0 approximate to 10(3)) that thermal motion induces optical frequency fluctuations larger than the intrinsic optical linewidth. The system thereby operates in a fully nonlinear regime, which pronouncedly impacts the optical response, displacement measurement and radiation pressure backaction. Specifically, we measure an apparent optical linewidth that is dominated by thermo-mechanically induced frequency fluctuations over a wide temperature range, and show that in this regime thermal displacement measurements cannot be described by conventional analytical models. We perform a proof-of-concept demonstration of exploiting the nonlinearity to conduct sensitive quadratic readout of nanomechanical displacement. Finally, we explore how backaction in this regime affects the mechanical fluctuation spectra.

European Research Council (ERC) , NWO
S.A. Mann (Sander)
Nature Commun.
Photonic Forces

Leijssen, R., La Gala, G., Freisem, L., Muhonen, J., & Verhagen, E. (2017). Nonlinear cavity optomechanics with nanomechanical thermal fluctuations. Nature Commun., 8(Article number: 16024), 1–10. doi:10.1038/ncomms16024