Effect of radiation damage on the quantum optical properties of nitrogen vacancies in diamond

Single crystal diamond (<5 ppm nitrogen) containing native NV centers with coherence time of 150 μs was irradiated with 2 MeV alpha particles, with doses ranging from 10¹² ion/cm² to 10¹⁵ ion/cm². The effect of ion damage on the coherence time of NV centers was studied using optically detected magnetic resonance and supplemented by fluorescence and Raman microscopy. A cross-sectional geometry was employed so that the NV coherence time could be measured as a function of increasing defect concentration along the ion track. Surprisingly, although the ODMR contrast was found to decrease with increasing ion induced vacancy concentration, the measured decoherence time remained undiminished at 150us despite the estimated vacancy concentration reaching a value of 40 ppm at the end of range. These results suggest that ion induced damage in the form of an increase in vacancy concentration does not necessarily result in a significant increase in the density of the background spin bath.