Forward four-wave mixing as an effective mechanism for generation of polychromatic correlated fields in a Λ medium

The forward four-wave-mixing (FWM) processes are considered in a typical three-level Λ scheme of electromagnetically induced transparency. The effective conversion of monochromatic drive radiation to the polychromatic field with correlated (entangled) components is predicted. The generation is characterized by narrow frequency band and low threshold for drive intensity. The nonlinear semiclassical analysis of the effect is presented. The two connected FWM processes are described via two-dimensional Hamiltonian with one varying parameter.