Propagation dynamics of a temporally, amplitude- and group-velocity-matched two-mode ultraslow wave in a three-level Λ system

We investigate the propagation dynamics of a two-mode probe field traveling with ultraslow group velocities. We show that a strong cross-beam coupling occurs between the two modes of the probe wave in the presence of a two-mode control laser field that maintains two-photon resonance excitations in a three-level Λ system. In the adiabatic limit and under appropriate conditions, both modes can travel with matched temporal profiles, amplitudes, and greatly reduced group velocities, and one mode can grow and take on features of the other mode. When only one mode of probe field is injected, the generation and growth of the second mode has the characteristics of four-wave mixing, resulting in a tunable, ultraslow four-wave mixing field with nearly 100% photon flux conversion efficiency. We further show a type of induced transparency resulting from an efficient one- and three-photon destructive interference. This is to be contrasted with the conventional one-mode, three-level electromagnetically induced transparency where the interference involves two one-photon pathways