Knob of the group velocity by the external field coupling two upper levels

摘要

We investigate how the external field coupling the two upper levels produces a variety of effects on the propagation of a weak electromagnetic pulse in a V-type atomic system. Due to the upper level (UL) coupling field, the dispersion of the system has been influenced by the relative phase. Then, subluminal and superluminal phenomena can be unified. Thus, the external field and the relative phase can be regarded as switches to manipulate light propagation between subluminal and superluminal.