A synthetic
single crystal diamond material comprising: a first region of synthetic
single crystal diamond material comprising a plurality of
electron donor defects; a second region of synthetic
single crystal diamond material comprising a plurality of
quantum spin defects; and a third region of synthetic
single crystal diamond material disposed between the first and second regions such that the first and second regions are spaced apart by the third region, wherein the second and third regions of synthetic
single crystal diamond material have a lower concentration of
electron donor defects than the first region of synthetic
single crystal diamond material, and wherein the first and second regions are spaced apart by a distance in a range 10 nm to 100 μm which is sufficiently close to allow electrons to be donated from the first region of synthetic single
crystal diamond material to the second region of synthetic single
crystal diamond material thus forming negatively charged
quantum spin defects in the second region of synthetic single
crystal diamond material and positively charged defects in the first region of synthetic single crystal diamond material while being sufficiently far apart to reduce other
coupling interactions between the first and second regions which would otherwise unduly reduce the decoherence time of the plurality of
quantum spin defects and / or produce strain broaden of a
spectral line width of the plurality of quantum spin defects in the second region of synthetic single crystal diamond material.