Optimum Photoluminescence Excitation and Recharging Cycle of Single Nitrogen-Vacancy Centers in Ultrapure Diamond

Important features in the spectral and temporal photoluminescence excitation of single nitrogen-vacancy (NV) centers in diamond are reported at conditions relevant for quantum applications. Bidirectional switching occurs between the neutral (NV⁰) and negatively charged (NV^-) states. Luminescence of NV^- is most efficiently triggered at a wavelength of 575 nm which ensures optimum excitation and recharging of NV⁰. The dark state of NV^- is identified as NV⁰. A narrow resonance is observed in the excitation spectra at 521 nm, which mediates efficient conversion to NV⁰.