Pump-Enhanced Continuous-Wave Magnetometry Using Nitrogen-Vacancy Ensembles

Ensembles of nitrogen-vacancy centers in diamond are a highly promisingplatform for high-sensitivity magnetometry, whose efficacy is often based onefficiently generating and monitoring magnetic-field dependent infraredfluorescence. Here we report on an increased sensing efficiency with the use ofa 532-nm resonant confocal cavity and a microwave resonator antenna formeasuring the local magnetic noise density using the intrinsic nitrogen-vacancyconcentration of a chemical-vapor deposited single-crystal diamond. We measurea near-shot-noise-limited magnetic noise floor of 200 pT√Hz spanning a bandwidth up to 159 Hz, and an extracted sensitivity ofapproximately 3 nT/√Hz, with further enhancement limited by thenoise floor of the lock-in amplifier and the laser damage threshold of theoptical components. Exploration of the microwave and optical pump-rateparameter space demonstrates a linewidth-narrowing regime reached by virtue ofusing the optical cavity, allowing an enhanced sensitivity to be achieved,despite an unoptimized collection efficiency of about 0.2 ppb.