Homogeneous spin-dephasing time of NV− centre in millimetre-scale 12C-enriched high-pressure high-temperature diamond crystals

Negatively charged nitrogen vacancy (NV−) centres in diamond crystals are promising colour centres for high-sensitivity quantum sensors. A long dephasing time (T2* > 10 μs) is essential for achieving increased sensitivity and higher uniformity of T2* in millimetre-scale diamond is strongly desired for femto-tesla weak magnetic field detection. High uniformity of T2* for NV− centres is achieved herein. The median value of T2*, <T2*>, in the 12C-enriched high-pressure, high-temperature (HPHT) grown diamond with a nitrogen concentration of 1.3 ± 0.4 ppm is 4.5 μs. The variance of T2* is only 10% over a millimetre-scale region (1.1 × 1.1 mm2) within the 0.4 mm thick {111} growth sector. <T2*> is ~2/3 times the value limited by the dipole-dipole interaction from the electron-spin bath of nitrogen impurities, suggesting that the residual strain gradient in the HPHT diamond crystal partially limits T2*. Reducing the strain gradient in diamond crystals provide a pathway to achievement of high sensitivity magnetometry using NV quantum sensing. Negatively charged nitrogen vacancy centres in diamond crystals are promising for achieving high-sensitivity quantum sensors. Here, a long dephasing time with high uniformity is achieved in a millimetre-scale area along the {111} plane using 12C enriched high-pressure high-temperature diamond crystals.