Dependence of NV-Ensemble T2* on Applied Magnetic Field

In measurements using ensembles of nitrogen vacancy (NV) centers in diamond,~the magnetic field sensitivity can be improved by~increasing the NV spin dephasing time, T2*.~ For NV ensembles, T2* is limited by inhomogeneous broadening arising from variations in the local environment sensed by individual NVs, such as magnetic fields and strain. Here, we describe a systematic study of parameters influencing the~NV ensemble~T2*, and efforts to mitigate sources~of inhomogeneity. In particular, we report a non-trivial dependence of T2* on applied external magnetic field.~These results suggest new pathways to improving the sensitivity of NV-ensemble magnetometry.~