Nonlinear cavity optomechanics with nanomechanical thermal fluctuations

Rick Leijssen,Ewold Verhagen,Lars Freisem,Juha T Muhonen,Giada R La Gala

doi:10.1038/ncomms16024

Rick Leijssen, Ewold Verhagen + Show 3 more

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https://doi.org/10.1038/ncomms16024

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Abstract

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 C0≈103) 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.

Highlights

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
It combines low-mass, megahertzfrequency, nanomechanical modes with subwavelength optical field confinement in a sliced photonic crystal nanobeam[36], to establish strong optomechanical interactions with photon–phonon coupling rates g0 in the range of tens of MHz
With the fabricated gap size of 45–50 nm, we simulated the optical frequency change due to a displacement of the beams to be @o/@x/2p 1⁄4 0.8 THz nm À 1, where xd/2. This leads to an expected optomechanical coupling rate of g0/2p 1⁄4 35 MHz

Summary

Introduction

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. The interaction between light in an optical cavity and the motion of a mechanical resonator enables sensitive optical readout of displacement, as well as manipulation of the motion of the resonator through optical forces[1] This has allowed demonstrations of sideband and feedback cooling of the mechanical resonator near its quantum ground state[2,3,4,5], squeezing of light[6,7,8] and of the mechanical zero-point fluctuations[9,10,11], entanglement[12] and state transfer[13] between the optical and mechanical degrees of freedom, as well as detection of radiation pressure shot noise[14,15] and non-classical correlations[16,17,18,19]. In the so-called bad-cavity limit (k4Om), the nonlinearity of the interaction provides a useful path towards creating motional quantum states, for example through performing quadratic measurements of displacement (proportional to ^x2)[23,24,25,26,27]

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