  Color centers in hexagonal boron nitride (hBN) are becoming an increasingly
important building block for quantum photonic applications. Herein, we
demonstrate the efficient coupling of recently discovered spin defects in hBN
to purposely designed bullseye cavities. We show that the all monolithic hBN
cavity system exhibits an order of magnitude enhancement in the emission of the
coupled boron vacancy spin defects. In addition, by comparative finite
difference time domain modelling, we shed light on the emission dipole
orientation, which has not been experimentally demonstrated at this point.
Beyond that, the coupled spin system exhibits an enhanced contrast in optically
detected magnetic resonance readout and improved signal to noise ratio. Thus,
our experimental results supported by simulations, constitute a first step
towards integration of hBN spin defects with photonic resonators for a scalable
spin photon interface.
