Relaxation Mechanisms of Single Dark Spins in Diamond*

Widespread adoption of the nitrogen vacancy (NV) center is diamond for quantum sensing requires understanding and mitigating spin decoherence. The substitutional nitrogen electron spin (P1 center) bath, introduced into the diamond lattice during NV center synthesis, is a dominant source of NV center decoherence, but an experimental picture of the underlying bath evolution remains incomplete. Here, we present a combined computational and experimental approach to engineer NV-bath interactions and measure the relaxation of individual P1 bath spins. First, cluster correlation expansion (CCE) calculations predict the growth conditions necessary to isolate single bath spin interactions. Furthermore, these calculations allow us to determine the spin bath structure around the NV center, enabling simulations of bath dynamics that account for local disorder. We then use the NV center to measure the evolution of P1 spins with a polarization pump-probe scheme. Time-resolved P1 measurements reveal charge and spin dynamics at the single-spin level.