Near-unity charge state initialization of NV centers in diamond using photo-activation of phosphorus dopants

Nitrogen vacancy (NV) centers in diamond are widely explored as quantum sensors and qubits because of their long coherence time, optical spin readout, and optical spin initialization in ambient conditions. However, the NV center suffers from imperfect charge state initialization, leading to state preparation and measurement errors around 30%. This poor charge state initialization arises from ionization and recombination under green excitation, leading to continuous charge cycling. A natural approach to circumvent this problem is to avoid direct excitation of the NV center and instead utilize itinerant carrier capture to prepare the charge state. Here we demonstrate that selective ionization of implanted phosphorous (P) donors using near-infrared excitation can enhance NV center charge state initialization to near-unity fidelity, with no decay in the charge population detectable out to 1.5 seconds. This initialization is effective even for NV centers that are located over 10 μm away from the P bath, making the contribution of P electronic spins to NV center decoherence negligible. Our work shows that the large difference between electronic and magnetic interaction length scales in high purity diamond can be exploited to produce tailored materials for quantum technologies.