Scalable Integration of Long-Lived Quantum Memories into a Photonic Circuit

We demonstrate a photonic circuit with integrated long-lived quantum memories. Precharacterized quantum nodes-diamond microwaveguides containing single, stable, negatively charged nitrogen-vacancy centers-are deterministically integrated into low-loss silicon nitride waveguides. These quantum nodes efficiently couple into the single-mode waveguides with >1 Mcps collected into the waveguide, have narrow single-scan linewidths below 400 MHz, and exhibit long electron spin coherence times up to 120 mu s. Our system facilitates the assembly of multiple quantum nodes with preselected properties into a photonic integrated circuit with near unity yield, paving the way towards the scalable fabrication of quantum information processors.