Dispersion relations for light propagation through a two-level system

Galina A. Nemova

Dingan Han, Yaguang Zeng, Yanfeng Bai +2 more

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.

Qiguang Yang, Jaetae Seo, Wei Gong +10 more

Chih-Chun Chang, Lee Lin, Guang-Yin Chen

In a quantum system of arrayed two-level atoms interacting with light, the interacted (dressed) photon is propagating in a periodic medium and its eigenstate ought to be of Bloch type with lattice symmetry. As the energy of photon is around the spacing between the two atomic energy levels, the photon will be absorbed and is not in the propagating mode but the attenuated mode. Therefore an energy gap exists in the dispersion relation of the photonic Bloch wave of dressed photon in addition to the nonlinear behaviors due to atom-light interactions. There follows several interesting results which are distinct from those obtained through a linear dispersion relation of free photon. For example, slow light can exist, the density of state of dressed photon is non-Lorentzian and is very large around the energy gap; the Rabi oscillations become monotonically decreasing in some cases; and besides the superradiance occurs at long wavelengths, the spontaneous emission is also very strong near the energy gap because of the high density of state.

Oleg N. Gadomsky, V. R. Nagibarov

Bang‐Pin Hou, Shun-Jin Wang, W L Yu +1 more

When the interactions of the two coupling transitions from an excited level to two nearly degenerate ground levels with the same vacuum occur in a four-level tripod-scheme atomic system, vacuum-induced coherence (VIC) results from the quantum interference between the two spontaneous transitions. We investigate the effects of VIC and the relative phase between the two coupling fields on the probe absorption and dispersion properties as well as the group velocity of the probe field. We find that by adjusting the incoherent pumping field and VIC as well as the relative phase, the central absorption peak in the double transparency spectrum reduces, even develops into a gain dip, and the probe field propagates at a velocity from superluminal to subluminal. It is particularly pointed out that the subluminal light propagation with gain without inversion can be realized in such a system. The physical interpretation of the phenomena has been given.