Real-Time Charge Initialization of Diamond Nitrogen-Vacancy Centers for Enhanced Spin Readout

Spin qubits based on nitrogen-vacancy centers in diamond are useful only when the defect exists in the correct charge state---but this state is usually uncontrolled, since it is sensitive to the optical fields used to interrogate the qubit. Using fast, real-time photon detection and control, the authors deterministically prepare the desired charge state and demonstrate that the qubit's performance as a magnetic sensor is dramatically improved. These experiments yield deeper understanding of the charge and spin dynamics of N-$V$ centers, and the all-optical method can be adapted to dynamically control other stochastic properties of solid-state defects for improved performance.