We present a theoretical model describing the magnetic-state population dynamics of spin-degenerate two-level atoms interacting with a narrowband, on-resonance, partially polarized electromagnetic field. The field is allowed to have three uncorrelated orthogonal vector components. The model is applied to a four-magnetic-state atom system with a single excited and three ground states. Even if the field is narrowband, the population dynamics may be completely predicated by the fluctuating polarization of light. In our examples, the fluctuation effects are mainly governed by a single parameter, the degree of polarization of the field.Peer reviewe
