Near-unity charge state initialization and better spin state readout of NV centers in diamond via multi-color excitation

Nitrogen-Vacancy (NV) centers in diamond are excellent quantum sensors for their long spin coherence times and optical spin readout under ambient conditions. However, they suffer from significant NV^- state preparation and measurement errors of up to 30%, due to charge dynamics under off-resonant green excitation. A promising method to mitigate this issue is multicolor excitation with green and near-infrared wavelengths, which alters the relative ionization and recombination rates to achieve 91% fidelity initialization [1]. Previous demonstrations of this approach required high excitation powers and extended exposure times. By rigorously analyzing experimental parameters, we identified conditions where simultaneous near-infrared (905 nm) and green (520 nm) illumination at moderate power achieves near-unity NV charge initialization within 10 μs. We show that this multicolor initialization not only maintains the spin polarization but also reduces readout noise compared to green initialization due to enhanced NV^- charge preparation fidelity. We also demonstrate that this technique is effective for state-of-the-art shallow NV centers, within 10 nm of the diamond surface. This increased initialization fidelity paves the way for high-fidelity multiplexed measurements [2] and measuring higher order correlation functions [3].

[1] Hopper, et al., Physical Review B 94, 241201 (2016)

[2] Cheng, et al., arXiv preprint arXiv:2408.11666 (2024)

[3] Rovny, et al., Science 378.6626 (2022): 1301-1305