  Two-dimensional hexagonal boron nitride offers intriguing opportunities for
advanced studies of light-matter interaction at the nanoscale, specifically for
realizations in quantum nanophotonics. Here, we demonstrate the engineering of
optically-addressable spin defects based on the negatively-charged boron
vacancy center. We show that these centers can be created in exfoliated
hexagonal boron nitride using a variety of focused ion beams (nitrogen, xenon
and argon), with nanoscale precision. Using a combination of laser and resonant
microwave excitation, we carry out optically detected magnetic resonance
spectroscopy measurements, which reveal a zero-field ground state splitting for
the defect of ~3.46 GHz. We also perform photoluminescence excitation
spectroscopy and temperature dependent photoluminescence measurements to
elucidate the photophysical properties of the center. Our results are important
for advanced quantum and nanophotonics realizations involving manipulation and
readout of spin defects in hexagonal boron nitride.
