Diamond sensors, detectors, and quantum devices

A thin plate of synthetic single crystal diamond material, the thin plate of synthetic single crystal diamond material having:

• a thickness in a range 100 nm to 50 μm;
• a concentration of negatively charged nitrogen-vacancy defects (NV−) equal to or greater than 100 ppb (parts-per-billion);
• a concentration of point defects other than the NV− defects of below 200 ppm (parts-per-million);
• a total nitrogen concentration equal to or greater than 10 ppm;
• a concentration of all non-nitrogen point defects equal to or less than 1 ppm;
• wherein at least one major face of the thin plate of synthetic single crystal diamond material comprises surface termination species which have zero nuclear spin and/or zero electron spin;
• and
• wherein the product of the concentration of NV− defects and decoherence time T2 in the thin plate of synthetic single crystal diamond material is at least 0.1 ppm μs.