Quantum-optical characterization of single-photon emitters created by MeV proton irradiation of HPHT diamond nanocrystals

Deterministic single-photon sources are a fundamental tool for several emerging applications in quantum sensing and quantum metrology. In these fields, the exploitation of individual quantum systems could significantly improve the current measuring capabilities and define a new generation of standard measure units. In addition, the availability of nanoscale-sized single-photon emitters is also of considerable interest, as it enables a further integration with external structures or biological samples. In this work, we investigate the role of MeV proton irradiation in the production of single-photon emitters based on the nitrogen-vacancy complex (NV center) in nanodiamonds (NDs). Powders of nitrogen-containing type Ib diamond nanocrystals with a median size distribution of 80 nm were irradiated with 2 MeV protons at 5 × 1013 cm−2 fluence with the purpose of creating vacancies and thus promote the formation of NV centers upon a subsequent thermal annealing. Following a suitable chemical processing, the ND powders were characterized in their opto-physical properties by means of a single-photon-sensitive confocal photoluminescence microscopy setup equipped with a “Hanbury Brown & Twiss” interferometer, enabling the measurement of the second-order autocorrelation function characterizing the PL emission. A comparison with two reference batches of unirradiated NDs powder, which only underwent the chemical, and the chemical and thermal treatment, respectively, enabled to assess the role of ion implantation in the production of single-photon sources.