Common-mode noise suppression of vector magnetometry using electromagnetically induced transparency

Warm vapor quantum sensors have shown sensitivity comparable to SQUIDs in measuring scalar magnetic field. Scalar sensors can be adapted to include measurement of magnetic field orientation but usually at the cost of scalar accuracy. Magnetometry using two-photon electromagnetically induced transparency resonances can provide both scalar accuracy and vector information but the limits to such measurements are not currently well-understood. Here we present a novel measurement scheme in multi-resonance EIT spectroscopy where the common-mode shifts of the resonance spectrum can be significantly suppressed by repeatedly probing the frequency difference between a pair of symmetrical resonances. Operating at the earth-like magnetic field strength of 50 μΤ, a <=200 pT/rtHz magnetometer sensitivity at 1 mHz and 10 pT/rfHz at 0.1 Hz has been achieved.