Geometric-phase magnetometry protocol To implement geometric-phase magnetometry, we use a modified version of an experimental protocol (“Berry sequence”) previously applied to a superconducting qubit9. In our realization, the NV spin sensor is placed in a superposition state by a π/2 pulse, where the driving frequency of the π/2 pulse is chosen to be resonant with the NV ms = 0 ↔ ms = + 1 transition at constant bias field Bbias (≈9.6 mT in our experiment) aligned with the NV axis.
