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 (T-2* > 10 mu s) is essential for achieving increased sensitivity and higher uniformity of T-2* in millimetre-scale diamond is strongly desired for femto-tesla weak magnetic field detection. High uniformity of T-2* for NV- centres is achieved herein. The median value of T-2*, <T-2*>, in the C-12-enriched high-pressure, high-temperature (HPHT) grown diamond with a nitrogen concentration of 1.3 +/- 0.4 ppm is 4.5 mu s. The variance of T-2* is only 10% over a millimetre-scale region (1.1 x 1.1 mm(2)) within the 0.4 mm thick {111} growth sector. <T-2*> is similar to 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 T-2*. Reducing the strain gradient in diamond crystals provide a pathway to achievement of high sensitivity magnetometry using NV quantum sensing.