Ensembles of nitrogen vacancy centres (NVCs) in diamond can be employed for sensitive magnetometry. In this work we present a fiber-coupled NVC magnetometer with an unshielded sensitivity of (30 ± 10) pT/Hz in a (10 - 500)-Hz frequency range. This sensitivity is enabled by a relatively high green-to-red photon conversion efficiency, the use of a [100] bias field alignment, microwave and lock-in amplifier (LIA) parameter optimisation, as well as a balanced hyperfine excitation scheme. Furthermore, a silicon carbide (SiC) heat spreader is used for microwave delivery, alongside low-strain 12C diamonds, one of which is placed in a second magnetically insensitive fluorescence collecting sensor head for common-mode noise cancellation. The magnetometer is capable of detecting signals from sources such as a vacuum pump up to 2 m away, with some orientation dependence but no complete dead zones, demonstrating its potential for use in remote sensing applications.
@article{arxiv.2211.09170,
title = {Fiber-coupled Diamond Magnetometry with an Unshielded 30 pT/$\sqrt{\textrm{Hz}}$ Sensitivity},
author = {S. M. Graham and A. T. M. A. Rahman and L. Munn and R. L. Patel and A. J. Newman and C. J. Stephen and G. Colston and A. Nikitin and A. M. Edmonds and D. J. Twitchen and M. L. Markham and G. W. Morley},
journal= {arXiv preprint arXiv:2211.09170},
year = {2023}
}