Rabi spectroscopy of nitrogen-vacancy (NV) ensembles in diamond for optical magnetometry*

We study the effect of microwave driving on the NV-centers ground state
triplet both theoretically and experimentally. Specifically, we focus on Rabi
spectroscopy of NV ensembles at zero and low magnetic fields taking the
advantage of multiple frequency scales and different selection rules of spin
transitions between the triplet states. The microwave excitation direction,
amplitude, and resonance offset provide the necessary means for addressing
the non-equivalent NV sub-ensembles, allowing to distinguish electric and
magnetic noise contributions to the NV decoherence. In our theoretical treatment,
we assume a stationary, Gaussian, and Markovian process for electric and magnetic
noise. Aiming at the NV ensemble-based magnetometry, we show that, by proper control
of microwave resonance offset, it is possible to reduce the strain- and electric-field induced
broadening of Rabi spectrum thus optimizing the magnetometer resolution and absolute
sensitivity. Theoretical predictions are compared against the experimental measurements
employing shallow ensemble of quasi-2D NV distribution (implanted ~20 nm deep in E-grade
diamond), and uniformly distributed NV ensemble in optical grade diamond.