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Journal of Modern Optics

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

Dingan Han, Yaguang Zeng, Yanfeng Bai, Weicheng Chen, H. Lu

Published Nov 30, 2007• 8 citations
Publisher

Abstract

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.

DOI
10.1080/09500340701322030

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Physical Review A•Mar 20, 2001•182 citations
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.
Propagation of an electromagnetic pulse through a dielectric slab doped with three-level ladder-type atomic systems is discussed. It is shown that the group velocity of the reflected and transmitted pulses can be switched from subluminal to superluminal light propagation by the thickness of the slab or the intensity of the coupling field. Furthermore, it is found that, in the presence of quantum interference, the reflected and transmitted pulses are completely phase dependent. So, the group velocity of the reflected and transmitted pulses can only be switched from subluminal to superluminal by adjusting the relative phase of the applied fields.
We show that the group velocity of a weak pulse can be manipulated by controlling the phases of two weak optical fields applied to a V-shaped three-level system. Such control can even cause the probe propagation to change from subluminal to superluminal. We consider two schemes: in the first, the excited states are coupled by decay-induced coherence, which is an inherent property of the medium, and in the second, quantum coherence is created by coupling the excited states to each other by a strong microwave field. We also discuss the group velocity reduction experienced by a single weak propagating probe due to decay-induced coherence.