Nonlinear optomechanical paddle nanocavities

TL;DR

This paper introduces a nanoscale paddle nanocavity with strong nonlinear optomechanical coupling, enabling potential quantum experiments by combining low mass, large optical mode spacing, and high nonlinear interaction strength.

Contribution

The work presents a novel paddle nanocavity design that achieves strong quadratic optomechanical coupling without relying on nearly degenerate optical modes.

Findings

Supports mechanical resonances with hundreds of femtogram mass

Achieves quadratic optomechanical coupling coefficient > 400 MHz/nm^2

Enables nonlinear readout of thermally driven motion at temperatures above 50 mK

Abstract

Nonlinear optomechanical coupling is the basis for many potential future experiments in quantum optomechanics (e.g., quantum non-demolition measurements, preparation of non-classical states), which to date have been difficult to realize due to small non-linearity in typical optomechanical devices. Here we introduce an optomechanical system combining strong nonlinear optomechanical coupling, low mass and large optical mode spacing. This nanoscale "paddle nanocavity" supports mechanical resonances with hundreds of fg mass which couple nonlinearly to optical modes with a quadratic optomechanical coupling coefficient $g^{(2)} > 2\pi\times400$ MHz/nm$^2$, and a two phonon to single photon optomechanical coupling rate $\Delta \omega_0 > 2\pi\times 16$ Hz. This coupling relies on strong phonon-photon interactions in a structure whose optical mode spectrum is highly non--degenerate. Nonlinear optomechanical readout of thermally driven motion in these devices should be observable for T $> 50 $ mK, and measurement of phonon shot noise is achievable. This shows that strong nonlinear effects can be realized without relying on coupling between nearly degenerate optical modes, thus avoiding parasitic linear coupling present in two mode systems.