Abstract

We exploit decay-induced interference effects in order to slow down light propagation. The system we investigate is a V-shaped closed three-level system, with lower level |1> and upper levels |2> > and |3>. The upper levels are coupled to the lower level by the vacuum modes. This interaction produces the usual relaxation processes of spontaneous emission from levels |2> and |3> to level |1>. However, when the splitting ω₃₂ between the upper levels |2> and |3> is much smaller than the transverse decay rates γ₂ and γ₃, one has also to consider interference effects due to spontaneous emission. The absorption of a single weak probe in this system has been shown to exhibit ultranarrow resonances [1]. When the upper levels are very close, the width of the transparency becomes subnatural and the dispersion very steep. We assume that the dipole moments μ₂₁ and μ₃₁ are parallel, in order to maximize the quantum coherence. The steep dispersion accompanying the transparency leads to group velocity reduction. A weak pulse of spectral width similar to the width of the transparency region propagates in the medium with a highly reduced group velocity. The group velocity is sensitive to the upper level splitting: the slope of the dispersion becomes steeper as ω₃₂ is reduced leading to decreased group velocity, as shown in Fig. 1. This slowing down of the group velocity is due to the coherence effects induced by the decay mechanism, which is an inherent property of the medium, rather than those induced by an externally applied field, as in electromagnetically induced transparency [2].

© 2000 IEEE