  The negatively-charged nitrogen vacancy center (NV) in diamond has generated
significant interest as a platform for quantum information processing and
sensing in the solid state. For most applications, high quality optical
cavities are required to enhance the NV zero-phonon line (ZPL) emission. An
outstanding challenge in maximizing the degree of NV-cavity coupling is the
deterministic placement of NVs within the cavity. Here, we report photonic
crystal nanobeam cavities coupled to NVs incorporated by a delta-doping
technique that allows nanometer-scale vertical positioning of the emitters. We
demonstrate cavities with Q up to ~24,000 and mode volume V ~
$0.47({\lambda}/n)^{3}$ as well as resonant enhancement of the ZPL of an NV
ensemble with Purcell factor of ~20. Our fabrication technique provides a first
step towards deterministic NV-cavity coupling using spatial control of the
emitters.
