Long coherence time of spin qubits in ¹²C enriched polycrystalline chemical vapor deposition diamond

Single defects in diamond and especially negatively charged nitrogen vacancy (NV) centers are very promising quantum systems with wide applications in physics and biology. It was shown that their coherence properties can be strongly improved by growing ultrapure diamond with low concentration of parasitic spins associated with nitrogen electron spins and nuclear spins related to ¹³C carbon isotope. Here we report a high quality ¹²C-enriched polycrystalline CVD diamond material with properties comparable with single crystals. We find single NVs in the grains of this material, which show extremely long electron spin coherence time T₂ > 2\,ms.