The nitrogen-vacancy (NV) centre in diamond is a leading platform for room-temperature quantum sensing. Improvements in sensitivity require precise control of the NV charge state. Transitions from the neutral NV0 charge state to the negative NV− charge state can occur during excitation with photon energies below the ZPL transition of NV0. These sub-resonant charge transitions limit modern initialisation protocols and have not been studied in full detail. In this paper we show that sub-resonant charge cycling arises from phonon-assisted anti-Stokes excitation. We further uncover the phonon states which contribute most strongly to the anti-Stokes transition via the development of novel quantitative models. The models indicate that low energy acoustic phonons strongly contribute to the transition close to the ZPL. At longer wavelengths a 43\,meV mode additionally impacts the charge cycling dynamics.
@article{arxiv.2605.07891,
title = {Phonon-assisted charge-cycling of nitrogen-vacancy centres in diamond},
author = {M. Olney-Fraser and J. Fuhrmann and S. Dietel and L. Kazak and F. Jelezko},
journal= {arXiv preprint arXiv:2605.07891},
year = {2026}
}