Nitrogen related paramagnetic defects: Decoherence source of ensemble of NV− center

We investigated spin-echo coherence times T2 of negatively charged nitrogen vacancy center (NV−) ensembles in single-crystalline diamond synthesized by either the high-pressure and high-temperature and chemical vapor deposition methods. This study specifically examined the magnetic dipole–dipole interaction (DDI) from the various electronic spin baths, which are the source of T2 decoherence. Diamond samples with NV− center concentration [NV−] comparable to those of neutral substitutional nitrogen concentration [Ns0] were used for DDI estimation. Results show that the T2 of the ensemble NV− center decreased in inverse proportion to the concentration of nitrogen-related paramagnetic defects [NPM], being the sum of [Ns0], [NV−], and [NV0], which is a neutrally charged state NV center. This inversely proportional relation between T2 and [NPM] indicates that the nitrogen-related paramagnetic defects of three kinds are the main decoherence source of the ensemble NV− center in the single-crystalline diamond. We found that the DDI coefficient of NVH− center was significantly smaller than that of Ns0, the NV0 center, or the NV− center. We ascertained the DDI coefficient of the NV− center [Formula: see text] through experimentation using a linear summation of the decoherence rates of each nitrogen-related paramagnetic defect. The obtained value of 89  μs ppm for [Formula: see text] corresponds well to the value estimated from the relation between DDI coefficient and spin multiplicity.