Enhanced DC-Field Metrology Using Nitrogen Vacancy Spins via Strong Collective Coupling and Fano-Scattering

Nitrogen-vacancy ensembles promise an unprecedented combination of sensitivity and resolution for magnetic field sensing under ambient conditions. However, their full sensing potential is limited by the inhomogeneous degradation of their collective coherence, while dynamical-decoupling limits sensing to the detection of AC-fields. Here we propose using the recently demonstrated cavity-protection effect for room-temperature, ensemble-based DC metrology. We identify a parameter space where strong-coupling can persist at room temperature and where the dressed states are limited solely by the dephasing of the cavity mode and the ensemble longitudinal relaxation, showing aT Hz$^{-\frac{1}{2}}$ DC-field sensitivities to be theoretically achievable with further augmentation through Fano-interference.