Ensembles of nitrogen-vacancy centers in diamond are a highly promising platform for high-sensitivity magnetometry, whose efficacy is often based on efficiently generating and monitoring magnetic-field dependent infrared fluorescence. Here we report on an increased sensing efficiency with the use of a 532-nm resonant confocal cavity and a microwave resonator antenna for measuring the local magnetic noise density using the intrinsic nitrogen-vacancy concentration of a chemical-vapor deposited single-crystal diamond. We measure a near-shot-noise-limited magnetic noise floor of 200 pT/Hz spanning a bandwidth up to 159 Hz, and an extracted sensitivity of approximately 3 nT/Hz, with further enhancement limited by the noise floor of the lock-in amplifier and the laser damage threshold of the optical components. Exploration of the microwave and optical pump-rate parameter space demonstrates a linewidth-narrowing regime reached by virtue of using the optical cavity, allowing an enhanced sensitivity to be achieved, despite an unoptimized collection efficiency of <2 %, and a low nitrogen-vacancy concentration of about 0.2 ppb.
@article{arxiv.1707.00502,
title = {Pump-Enhanced Continuous-Wave Magnetometry using Nitrogen-Vacancy Ensembles},
author = {Sepehr Ahmadi and Haitham A. R. El-Ella and Jørn O. B. Hansen and Alexander Huck and Ulrik L. Andersen},
journal= {arXiv preprint arXiv:1707.00502},
year = {2017}
}