Cross-relaxation studies with optically detected magnetic resonances in nitrogen-vacancy centers in diamond in external magnetic field

Abstract

In this work, cross relaxation between nitrogen-vacancy (NV) centers and substitutional nitrogen in a diamond crystal is investigated. It is demonstrated that optically detected magnetic resonance signals (ODMR) can be used to probe cross relaxation. ODMR is detected at axial magnetic field values around 51.2 mT in a diamond sample with a relatively high (200 ppm) nitrogen concentration. We observe transitions that involve magnetic sublevels that are split by the hyperfine interaction. Microwaves in the frequency ranges from 1.3 GHz to 1.6 GHz (${m}_{S}=0\ensuremath{\longrightarrow}{m}_{S}=\ensuremath{-}1$ NV transitions) and from 4.1 to 4.6 GHz (${m}_{S}=0\ensuremath{\longrightarrow}{m}_{S}=+1$ NV transitions) were used. To understand the cross-relaxation process in more detail and, as a result, reproduce measured signals more accurately, a model is developed that describes the microwave-initiated transitions between hyperfine levels of the NV center at anticrossing that are strongly mixed. Additionally, we simulate the extent to which the microwave radiation driving ODMR in the NV center also induces transitions in the substitutional nitrogen via cross relaxation. The improved understanding of the NV processes in the presence of magnetic field will be useful for designing NV-diamond-based devices for a wide range of applications from implementation of q bits to hyperpolarization of large molecules to various quantum technological applications such as field sensors.