  Resonantly enhanced emission from the zero phonon line of a diamond
nitrogen-vacancy (NV) center in single crystal diamond is demonstrated
experimentally using a hybrid whispering gallery mode nanocavity. A 900 nm
diameter ring nanocavity formed from gallium phosphide, whose sidewalls extend
into a diamond substrate, is tuned onto resonance at low-temperature with the
zero phonon line of a negatively charged NV center implanted near the diamond
surface. When the nanocavity is on resonance, the zero phonon line intensity is
enhanced by approximately an order of magnitude, and the spontaneous emission
lifetime of the NV is reduced as much as 18%, corresponding to a 6.3X
enhancement of emission in the zero photon line.
