Nonlinear cavity optomechanics with nanomechanical thermal fluctuations

TL;DR

This paper demonstrates a nanoscale cavity optomechanical system operating in a fully nonlinear regime where thermal fluctuations significantly affect optical properties, revealing new behaviors and measurement capabilities.

Contribution

The work introduces a highly nonlinear optomechanical system with large single-photon cooperativity, showing thermal motion induces dominant optical frequency fluctuations and enabling quadratic position measurements.

Findings

Thermal motion causes optical linewidth broadening.

Nonlinear regime invalidates traditional displacement measurement models.

Quadratic position measurement with suppressed linear transduction.

Abstract

The inherently nonlinear interaction between light and motion in cavity optomechanical systems has experimentally been studied in 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 $C_0 \approx 10^3$) 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. Experiments show that the apparent optical linewidth is dominated by thermomechanically-induced frequency fluctuations over a wide temperature range. The nonlinearity induces breakdown of the traditional cavity optomechanical descriptions of thermal displacement measurements. Moreover, we explore how radiation pressure backaction in this regime affects the mechanical fluctuation spectra. The strong nonlinearity could serve as a resource to control the motional state of the resonator. We demonstrate the use of highly nonlinear transduction to perform a quadratic measurement of position while suppressing linear transduction.