Abstract
Coherent population trapping resonances in cesium vapor can be used to determine DC flux densities in the range from 1 μT to 1 mT with typically 3·10−5 relative uncertainty. For fields modulated at a few kHz, we find sensitivities of below 10 pT within 0.5 s integration time. From the signal-to-noise ratio the sensitivity can be extrapolated to 500 fT/√Hz. A quantitative understanding of the lineshape allows to detect DC fields of several nT even when the Zeeman components of the resonance are not resolved.