Description
Nitrogen-vacancy (NV) centres are emerging as a powerful platform for magnetic field sensing. However, the bias field required by most state-of-the-art NV vector magnetometers severely limits their deployable sensitivity beyond the ($\mathrm{nT/\sqrt{Hz}}$) range, as thermal and mechanical drifts of the bias field are indistinguishable from changes in the measured field. Furthermore, many magnetometry applications require operation in the zero-to-ultra-low-field (ZULF) regime to avoid perturbing the sample. In these applications, NV centres are highly attractive due to diamond's biological compatibility, thermal stability, and other unique material properties. However, their reliance on relatively large bias fields currently renders them unsuitable for ZULF operation.
The development of a bias-free NV magnetometer requires overcoming two major challenges: the zero-field degeneracy of the electronic spin states and the strain-induced weakly sensitive quadratic Zeeman regime. While strain suppresses conventional Zeeman-based sensing at zero field, the resulting strain-induced superposition of the ($\mathrm{S_z}$) states presents an alternative sensing modality. Near zero field, the relative ($\mathrm{S_z}$) composition of these superposition states varies sharply with magnetic field. Circularly polarised microwaves resonant with one of the two zero-field transitions selectively drive either the ($m_s$=+1) or ($m_s$=-1) component, revealing the superposition structure of the strained electronic spin states. This superposition structure provides a sensitive proxy for the magnetic field along the NV axis. Furthermore, the interaction of polarised microwaves with each crystallographic NV orientation differs in an ensemble, enabling vector magnetic field measurements. By combining these techniques, truly bias-free NV vector magnetometry can be achieved.
| I am the presenting author | Yes |
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