Detection and Modeling of Hole Capture by Single Point Defects under Variable Electric Fields.

Understanding carrier trapping in solids has proven key to semiconductor technologies, but observations thus far have relied on ensembles of point defects, where the impact of neighboring traps or carrier screening is often important. Here, we investigate the capture of photogenerated holes by an individual negatively charged nitrogen-vacancy (NV) center in diamond at room temperature. Using an externally gated potential to minimize space-charge effects, we find the capture probability under electric fields of variable sign and amplitude shows an asymmetric-bell-shaped response with maximum at zero voltage. To interpret these observations, we run semiclassical Monte Carlo simulations modeling carrier trapping through a cascade process of phonon emission and obtain electric-field-dependent capture probabilities in good agreement with experiment. Because the mechanisms at play are insensitive to the characteristics of the trap, we anticipate the capture cross sections we observe─largely exceeding those derived from ensemble measurements─may also be present in materials platforms other than diamond.

Spin Dynamics of a Solid-State Qubit in Proximity to a Superconductor.

A broad effort is underway to understand and harness the interaction between superconductors and spin-active color centers with an eye on hybrid quantum devices and novel imaging modalities of superconducting materials. Most work, however, overlooks the interplay between either system and the environment created by the color center host. Here we use a diamond scanning probe to investigate the spin dynamics of a single nitrogen-vacancy (NV) center proximal to a superconducting film. We find that the presence of the superconductor increases the NV spin coherence lifetime, a phenomenon we tentatively rationalize as a change in the electric noise due to a superconductor-induced redistribution of charge carriers near induced redistribution of charge carriers near the NV. We then build on these findings to demonstrate transverse-relaxation-time-weighted imaging of the superconductor film. These results shed light on the dynamics governing the spin coherence of shallow NVs, and promise opportunities for new forms of noise spectroscopy and imaging of superconductors.

Room-Temperature Photochromism of Silicon Vacancy Centers in CVD Diamond.

The silicon vacancy (SiV) center in diamond is typically found in three stable charge states, SiV0, SiV-, and SiV2-, but studying the processes leading to their formation is challenging, especially at room temperature, due to their starkly different photoluminescence rates. Here, we use confocal fluorescence microscopy to activate and probe charge interconversion between all three charge states under ambient conditions. In particular, we witness the formation of SiV0 via the two-step capture of diffusing, photogenerated holes, a process we expose both through direct SiV0 fluorescence measurements at low temperatures and confocal microscopy observations in the presence of externally applied electric fields. In addition, we show that continuous red illumination induces the converse process, first transforming SiV0 into SiV- and then into SiV2-. Our results shed light on the charge dynamics of SiV and promise opportunities for nanoscale sensing and quantum information processing.

Imaging dark charge emitters in diamond via carrier-to-photon conversion.

The application of color centers in wide-bandgap semiconductors to nanoscale sensing and quantum information processing largely rests on our knowledge of the surrounding crystalline lattice, often obscured by the countless classes of point defects the material can host. Here, we monitor the fluorescence from a negatively charged nitrogen-vacancy (NV−) center in diamond as we illuminate its vicinity. Cyclic charge state conversion of neighboring point defects sensitive to the excitation beam leads to a position-dependent stream of photo-generated carriers whose capture by the probe NV− leads to a fluorescence change. This "charge-to-photon" conversion scheme allows us to image other individual point defects surrounding the probe NV, including nonfluorescent "single-charge emitters" that would otherwise remain unnoticed. Given the ubiquity of color center photochromism, this strategy may likely find extensions to material systems other than diamond.

Long-Term Spin State Storage Using Ancilla Charge Memories.

We articulate confocal microscopy and electron spin resonance to implement spin-to-charge conversion in a small ensemble of nitrogen-vacancy (NV) centers in bulk diamond and demonstrate charge conversion of neighboring defects conditional on the NV spin state. We build on this observation to show time-resolved NV spin manipulation and ancilla-charge-aided NV spin state detection via integrated measurements. Our results hint at intriguing opportunities in the development of novel measurement strategies in fundamental science and quantum spintronics as well as in the search for enhanced forms of color-center-based metrology down to the limit of individual point defects.

Probing Metastable Space-Charge Potentials in a Wide Band Gap Semiconductor.

While the study of space-charge potentials has a long history, present models are largely based on the notion of steady state equilibrium, ill-suited to describe wide band gap semiconductors with moderate to low concentrations of defects. Here we build on color centers in diamond both to locally inject carriers into the crystal and probe their evolution as they propagate in the presence of external and internal potentials. We witness the formation of metastable charge patterns whose shape-and concomitant field-can be engineered through the timing of carrier injection and applied voltages. With the help of previously crafted charge patterns, we unveil a rich interplay between local and extended sources of space-charge field, which we then exploit to show space-charge-induced carrier guiding.