Microring resonators on a suspended membrane circuit for atom-light interactions

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 (around 16 μm) microring and racetrack resonators with a high quality factor (Q) of 3.2×10⁵, projecting a single atom cooperativity parameter (C) of 25 and a vacuum Rabi frequency (2g) of 2π×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 5×10⁶, potentially achieving single atom cooperativity parameter higher than 500 for strong single atom-photon coupling.