  In search of two level quantum systems that implement a qubit, the
nitrogen-vacancy (NV) center in diamond has been intensively studied for years.
Despite favorable properties such as remarkable defect spin coherence times,
the addressability of NV centers raises some technical issues. The coupling of
a single NV center to an external driving field is limited to short distances,
since an efficient coupling requires the NV to be separated by only a few
microns away from the source. As a way to overcome this problem, an enhancement
of coherent coupling between NV centers and a microwave field has recently been
experimentally demonstrated using spin waves propagating in an adjacent yttrium
iron garnet (YIG) film [1]. In this paper we analyze the optically detected
magnetic resonance spectra that arise when an NV center is placed on top of a
YIG film for a geometry similar to the one in the experiment. We analytically
calculate the oscillating magnetic field of the spin wave on top of the YIG
surface to determine the coupling of spin waves to the NV center. We compare
this coupling to the case when the spin waves are absent and the NV center is
driven only with the antenna field and show that the calculated coupling
enhancement is dramatic and agrees well with the one obtained in the recent
experiment.
