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Bias-Field-Free Operation of Nitrogen-Vacancy Ensembles in Diamond for Accurate Vector Magnetometry

Lilian Childress1,*, Vincent Halde2,†, Kayla Johnson2, Andrew Lowther2, David Roy-Guay2, Romain Ruhlmann2, and Adrian Solyom2

  • 1Department of Physics, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8, Canada
  • 2SBQuantum, 805 Rue Galt O, Sherbrooke, Quebec J1H 1Z1, Canada

  • *Contact author: lilian.childress@mcgill.ca
  • †Contact author: vincent.halde@sbquantum.com
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PRX Quantum 6, 040364 – Published 15 December, 2025

DOI: https://doi.org/10.1103/zcdm-5qq3

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 subnanotesla 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 the 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.

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Physics Subject Headings (PhySH)

Popular Summary

Accurate, drift-free measurements of terrestrial magnetic fields’ magnitude and direction are essential to geoscience, navigation, and mineral exploration, but existing portable vector magnetometers are significantly less accurate than their scalar counterparts. Nitrogen-vacancy (NV) spins in diamond offer a new platform with native vector sensing thanks to their four possible orientations in the crystal, with each responding to distinct field components. Reconstruction of the vector field, however, requires isolation of signals from each orientation within the ensemble and assignment of their axis. The conventional solution—a dc bias magnetic field—leaves the magnetometer susceptible to inaccuracy induced by bias drifts that are indistinguishable from external fields. Our work identifies a robust mechanism for bias-field-free vector NV magnetometry.

In our approach, the NV spins are excited by two pulses of a microwave field whose polarization determines a distinct rate of driven spin oscillations for each orientation. Between pulses, the spins precess in the external magnetic field. By independently varying both the pulse duration and the interpulse delay, we can correlate the driven oscillation frequency (and thus orientation) with the component of the magnetic field along that axis, allowing extraction of field projections along known directions. Numerical simulations show that this technique is compatible with state-of-the-art vector accuracy even when the polarization of the microwave field is imprecisely calibrated, and preliminary experimental tests reveal expected features and evolution with the external field.

Our findings thus overcome a key barrier to accuracy in NV sensors, opening the door to drift-free, portable vector magnetometry.

Article Text

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PRX Quantum 6, 040364– Published 15 December, 2025
  • Received 30 May 2025
  • Revised 25 July 2025
  • Accepted 17 October 2025
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