Phase control of group velocity: From subluminal to superluminal light propagation

The phase control of two weak optical fields applied to a V-shaped three-level system was used to manipulate the group velocity of weak optical pulses. The phase control was applied to the schemes during the coupling of excited states by their interaction with the vacuum. The quantum coherence was created by coupling the two close-lying excited states by a strong microwave field. The group velocity reduction experienced by a single weak propagating probe due to decay-induced coherence was also discussed.