Zero-Field Magnetometry Based on Nitrogen-Vacancy Ensembles in Diamond

High-sensitivity magnetometry using ensembles of nitrogen-vacancy (N-V) centers in diamond has garnered broad interest lately. This technique typically requires a bias field to resolve magnetically sensitive features in the N-V level structure---a requirement that has hindered the adoption of N-V magnetometry in situations requiring zero ambient field. The authors overcome the need for a bias field by using circularly polarized microwaves to selectively address overlapping transitions in a ¹³C-depleted diamond. This approach offers a different avenue for applying N-V magnetometry, from zero- and ultralow-field nuclear magnetic resonance (ZULF-NMR) to biomagnetic measurements.