Pulse matching and correlation of phase fluctuations in Λ systems

The interaction of a bichromatic quantized field with three-level Λ-type atoms is analyzed on the basis of c-number Langevin equations. In the presence of ground-state coherence one particular combination of field modes is selectively absorbed leading to a correlation of the output fields. This correlation manifests itself in a matching of Fourier components of the field modes and in a strong reduction of the diffusion of the difference phase. This correlation phenomenon is studied for the case of externally generated coherence as well as for coherence produced by population trapping in conjunction with a nonadiabatic atomic response.