Scalable, nanoscale positioning of highly coherent color centers in prefabricated diamond nanostructures

Diamond nanophotonic devices leverage an enhanced coupling between their embedded color centers and the engineered photonic modes for efficient readout, control, and entanglement of their spin states. However, control over the formation of the color centers in position, density, and coherence remains a dominating limitation towards scalability. Here, we report a scalable method for creating highly coherent nitrogen-vacancy (NV) centers in prefabricated nanostructures with nanoscale localization precision. We combine nitrogen-delta doping during chemical vapor deposition (CVD) diamond growth with localized (beam spot size ~ 20 nm) 200 keV electron irradiation to form shallow NV centers (~50 nm-deep) aligned to the center of prefabricated diamond nanopillars. With control over electron dosage and annealing time, we demonstrate lateral positioning precision of < 120 nm and vertical precision of 4 nm with wide tunability over the number of NVs spanning two orders of magnitude. Our method results in NV centers with several favorable properties: pillars with single NV centers show a reproducibly long spin coherence time (average Hahn echo T2 of 98 μs) and an optimal coupling to the nanopillar with saturation photoluminescence (PL) (average of 1.1 Mcps) with a high spin-dependent PL contrast (average of 18 %). Our work will enable a high-yield production of diamond quantum sensors and processors with commercially available tools.