This paper provides an entropy analysis to resonant and short pulses propagation in four-level atomic medium. As an example, we take D_{1} transition in rubidium ^{87}Rb atoms including hyperfine structure. We show how to construct the time dependent Bloch-metric for each optical transition in the Liouville space. Furthermore, we attempt to relate local stabilization of the pulse area to the distribution of the space-entropy.
We analyse the three-colour electromagnetically induced transparency for the D_1 transition in cold ^{87}Rb atoms. We report an enhancement of the electromagnetically induced emission of a drive field as an exclusive enhancement of the third- and fourth-rank components of the density matrix. Moreover, the gain experienced by the drive field is attributed to the influence of the quantum switching effect on the increased absorption of the probe field. The electromagnetically induced emission effect is employed to generate slow light Gaussian-wave trains with shape preserving. These soliton trains were not only generated in the drive channel as has been designated but also in the switch channel which reveals multiple-light storage phenomenon.
The phase and group velocities of the pulsed light are suitably defined and calculated. So are the duration of both pulses, probe and coupling, and their energies as a function of the travelled distance. The time evolution, for a given distance, of the dressed atom state is described by the Liouville-von Neumann equation for the density matrix.
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