# Air mode silicon nitride photonic crystals and their application to nonlinear quantum optomechanical sensing

## TL;DR

This paper introduces a silicon nitride air-mode photonic crystal cavity with high optical quality and strong nonlinear coupling, advancing quantum optomechanical sensing capabilities for detecting nanomechanical phenomena.

## Contribution

It presents a novel design of air-mode photonic crystal cavities in silicon nitride nanobeams, enabling enhanced optomechanical coupling for quantum sensing applications.

## Key findings

- Achieved ultrahigh optical quality factor $Q_o\,\sim\,10^6$ in the cavity.
- Demonstrated quadratic coupling coefficient $g^{(2)}/2\pi = 10$ MHz/nm$^{2}$.
- Analyzed performance for quantum optomechanics experiments.

## Abstract

Nanoscale photonic crystal cavity optomechanical devices enable detection of nanomechanical phenomena with a sensitivity sufficient to observe quantum effects. Here we present the design of a one-dimensional air-mode photonic crystal cavity patterned in a silicon nitride nanobeam, and show that it forms the basis for cavity optomechanical split-beam and paddle nanocavity devices useful for force detection and nonlinear quantum sensing. The air-mode of this device is advantageous for optomechanical coupling, while also having ultrahigh optical quality factor $Q_o\sim 10^6$ despite its proximity to the light-line and the relatively low refractive index of silicon nitride. Paddle nanocavities realized from this device have a quadratic coupling coefficient $g^{(2)}/2\pi$~=~10~MHz/nm$^{2}$, and their performance within the context of quantum optomechanics experiments is analyzed.