  Diamond has emerged as a leading host material for solid-state quantum
emitters, quantum memories, and quantum sensors. However, the challenges in
fabricating photonic devices in diamond have limited its potential for use in
quantum technologies. While various hybrid integration approaches have been
developed for coupling diamond color centers with photonic devices defined in a
heterogeneous material, these methods suffer from either large insertion loss
at the material interface or evanescent light-matter coupling. Here, we present
a new technique that enables deterministic assembly of diamond color centers in
a silicon nitride photonic circuit. Using this technique, we observe Purcell
enhancement of silicon vacancy centers coupled to a silicon nitride ring
resonator. Our hybrid integration approach has the potential for achieving the
maximum possible light-matter interaction strength while maintaining low
insertion loss, and paves the way towards scalable manufacturing of large-scale
quantum photonic circuits integrated with high-quality quantum emitters and
spins.
