Bias-field-free operation of nitrogen-vacancy ensembles in diamond for accurate vector magnetometry

TL;DR

This paper introduces a bias-field-free method for NV ensemble magnetometry that enhances accuracy and stability, enabling precise vector magnetic field measurements without the need for a bias magnetic field.

Contribution

The authors develop a novel microwave field-based labeling technique in a Ramsey sequence to eliminate the need for bias magnetic fields in NV magnetometry.

Findings

Numerical simulations show sub-nT accuracy in terrestrial fields without MW calibration.

Experimental validation confirms the method's effectiveness and expected behavior.

The approach reduces drift, improving long-term stability of NV magnetometers.

Abstract

Accurate measurement of vector magnetic fields is critical for applications including navigation, geoscience, and space exploration. Nitrogen-vacancy (NV) center spin ensembles offer a promising solution for high-sensitivity vector magnetometry, as their different orientations in the diamond lattice measure different components of the magnetic field. However, the bias magnetic field typically used to separate signals from each NV orientation introduces inaccuracy from drifts in permanent magnets or coils. Here, we present a novel bias-field-free approach that labels the NV orientations via the direction of the microwave (MW) field in a variable-pulse-duration Ramsey sequence used to manipulate the spin ensemble. Numerical simulations demonstrate the possibility to isolate each orientation's signal with sub-nT accuracy in most terrestrial fields, even without precise MW field calibration, at only a moderate cost to sensitivity. We also provide proof-of-principle experimental validation, observing relevant features that evolve as expected with applied magnetic field. Looking forward, by removing a key source of drift, the proposed protocol lays the groundwork for future deployment of NV magnetometers in high-accuracy or long-duration missions.