Group IV vacancy color centers in diamond are promising spin-photon interfaces with strong potential for applications in photonic quantum technologies. Reliable methods for controlling and stabilizing their charge state are urgently needed for scaling to multiqubit devices. Here, we manipulate the charge state of silicon vacancy (SiV) ensembles by combining luminescence and photocurrent spectroscopy. We controllably convert the charge state between the optically active SiV- and dark SiV2- with megahertz rates and >90% contrast by judiciously choosing the local potential applied to in-plane surface electrodes and the laser excitation wavelength. We observe intense SiV- photoluminescence under hole capture, measure the intrinsic conversion time from the dark SiV2- to the bright SiV- to be 36.4(67) ms, and demonstrate how it can be enhanced by a factor of 105 via optical pumping. Moreover, we obtain previously unknown information on the defects that contribute to photoconductivity, indicating the presence of substitutional nitrogen and divacancies.

Quantum sensing with spin defectsin diamond, such asthe nitrogenvacancy (NV) center, enables the detection of various chemical specieson the nanoscale. Molecules or ions with unpaired electronic spinsare typically probed by their influence on the NV center'sspin relaxation. Whereas it is well-known that paramagnetic ions reducethe NV center's relaxation time (T (1)), here we report on the opposite effect for diamagnetic ions. Wedemonstrate that millimolar concentrations of aqueous diamagneticelectrolyte solutions increase the T (1) timeof near-surface NV center ensembles compared to pure water. To elucidatethe underlying mechanism of this surprising effect, single and doublequantum NV experiments are performed, which indicate a reduction ofmagnetic and electric noise in the presence of diamagnetic electrolytes.In combination with ab initio simulations, we proposethat a change in the interfacial band bending due to the formationof an electric double layer leads to a stabilization of fluctuatingcharges at the interface of an oxidized diamond. This work not onlyhelps to understand noise sources in quantum systems but could alsobroaden the application space of quantum sensors toward electrolytesensing in cell biology, neuroscience, and electrochemistry.

Materials combining semiconductor functionalities with spin control are desired for the advancement of quantum technologies. Here, we study the magneto-optical properties of novel paramagnetic Ruddlesden-Popper hybrid perovskites Mn:(PEA)2PbI4 (PEA = phenethylammonium) and report magnetically brightened excitonic luminescence with strong circular polarization from the interaction with isolated Mn2+ ions. Using a combination of superconducting quantum interference device (SQUID) magnetometry, magneto-absorption and transient optical spectroscopy, we find that a dark exciton population is brightened by state mixing with the bright excitons in the presence of a magnetic field. Unexpectedly, the circular polarization of the dark exciton luminescence follows the Brillouin-shaped magnetization with a saturation polarization of 13% at 4 K and 6 T. From high-field transient magneto-luminescence we attribute our observations to spin-dependent exciton dynamics at early times after excitation, with first indications for a Mn-mediated spin-flip process. Our findings demonstrate manganese doping as a powerful approach to control excitonic spin physics in Ruddlesden-Popper perovskites, which will stimulate research on this highly tuneable material platform with promise for tailored interactions between magnetic moments and excitonic states.