  Efficient interfaces between photons and quantum emitters form the basis for
quantum networks and enable nonlinear optical devices operating at the
single-photon level. We demonstrate an integrated platform for scalable quantum
nanophotonics based on silicon-vacancy (SiV) color centers coupled to nanoscale
diamond devices. By placing SiV centers inside diamond photonic crystal
cavities, we realize a quantum-optical switch controlled by a single color
center. We control the switch using SiV metastable orbital states and verify
optical switching at the single-photon level by using photon correlation
measurements. We use Raman transitions to realize a single-photon source with a
tunable frequency and bandwidth in a diamond waveguide. Finally, we create
entanglement between two SiV centers by detecting indistinguishable Raman
photons emitted into a single waveguide. Entanglement is verified using a novel
superradiant feature observed in photon correlation measurements, paving the
way for the realization of quantum networks.
