Shallow Silicon Vacancy Centers with Lifetime-Limited Optical Linewidths in Diamond Nanostructures.

The negatively charged silicon vacancy center (SiV-) in diamond is a promising, yet underexplored candidate for single-spin quantum sensing at sub-kelvin temperatures and tesla-range magnetic fields. A key ingredient for such applications is the ability to perform all-optical, coherent addressing of the electronic spin of near-surface SiV- centers. We present a robust and scalable approach for creating individual, ∼50 nm deep SiV- with lifetime-limited optical linewidths in diamond nanopillars through an easy-to-realize and persistent optical charge-stabilization scheme. The latter is based on single, prolonged 445 nm laser illumination that enables continuous photoluminescence excitation spectroscopy without the need for any further charge stabilization or repumping. Our results constitute a key step toward the use of near-surface, optically coherent SiV- for sensing under extreme conditions, and offer a powerful approach for stabilizing the charge-environment of diamond color centers for quantum technology applications.

Temperature-Dependent Photophysics of Single NV Centers in Diamond.

We present a comprehensive study of the temperature- and magnetic-field-dependent photoluminescence (PL) of individual NV centers in diamond, spanning the temperature-range from cryogenic to ambient conditions. We directly observe the emergence of the NV's room-temperature effective excited-state structure and provide a clear explanation for a previously poorly understood broad quenching of NV PL at intermediate temperatures around 50 K, as well as the subsequent revival of NV PL. We develop a model based on two-phonon orbital averaging that quantitatively explains all of our findings, including the strong impact that strain has on the temperature dependence of the NV's PL. These results complete our understanding of orbital averaging in the NV excited state and have significant implications for the fundamental understanding of the NV center and its applications in quantum sensing.

Low-Temperature Photophysics of Single Nitrogen-Vacancy Centers in Diamond.

We investigate the magnetic field dependent photophysics of individual nitrogen-vacancy (NV) color centers in diamond under cryogenic conditions. At distinct magnetic fields, we observe significant reductions in the NV photoluminescence rate, which indicate a marked decrease in the optical readout efficiency of the NV's ground state spin. We assign these dips to excited state level anticrossings, which occur at magnetic fields that strongly depend on the effective, local strain environment of the NV center. Our results offer new insights into the structure of the NVs' excited states and a new tool for their effective characterization. Using this tool, we observe strong indications for strain-dependent variations of the NV's orbital g factor, obtain new insights into NV charge state dynamics, and draw important conclusions regarding the applicability of NV centers for low-temperature quantum sensing.