  Individual spins that are coupled to telecommunication photons offer unique
promise for distributed quantum information processing once a coherent and
efficient spin-photon interface can be fabricated at scale. We implement such
an interface by integrating erbium dopants into a nanophotonic silicon
resonator. We achieve spin-resolved excitation of individual emitters with <
0.1 GHz spectral diffusion linewidth. Upon resonant driving, we observe optical
Rabi oscillations and single-photon emission with a 78-fold Purcell
enhancement. Our results establish a promising new platform for quantum
networks.
