# Microring resonators on a membrane optical circuit for atom-light interactions

## TL;DR

This paper presents the design and fabrication of silicon nitride microring resonators on a membrane platform, enabling strong atom-light interactions suitable for quantum hybrid systems.

## Contribution

It introduces a scalable, membrane-based photonic platform with high-Q microring resonators compatible with cold atom experiments and discusses pathways to enhance performance.

## Key findings

- High quality factor $Q=3.2\times 10^5$ achieved
- Projected single atom cooperativity $C=25$
- Potential to reach $Q>5\times10^6$ and $C>500$

## Abstract

We describe the design and fabrication of a scalable atom-light photonic interface based on a silicon nitride microring resonator on a transparent silicon dioxide-nitride multi-layer membrane. This new photonic platform is fully compatible with freespace cold atom laser cooling, stable trapping, and sorting at around $100~$nm from the microring surface, permitting the formation of an organized, strongly interacting atom-photonic hybrid lattice. We demonstrate small radius ($R\sim$16$\mu$m) microring and racetrack resonators with a high quality factor $Q=3.2\times 10^5$, projecting a single atom cooperativity parameter of $C=25$ and a vacuum Rabi frequency of $2g= 2\pi\times 340~$MHz for trapped cesium atoms interacting with a microring resonator mode. We show that the quality factor is currently limited by the surface roughness of the multi-layer membrane, grown using low pressure chemical vapor deposition (LPCVD) processes. We discuss possible further improvements to a quality factor above $Q>5\times10^6$, potentially achieving single atom cooperativity parameter of $C > 500$ for strong single atom-photon coupling.