Investigation on spontaneously generated coherence

Hermann Haken, R. Hübner, Karl Zeile

Wang Chun-liang

Spontaneously Generated Coherence(SGC) refers to a kind of quantum coherence induced by the process of spontaneous emission. It can greatly affect the dynamics of a quantum system, and accounts for a variety of important phenomena. Many efforts have been devoted to this topic, aiming to investigate the essence of quantum coherence and advanced technologies. However, the existence of SGC needs rigorous requirements which can hardly been fulfilled in atoms placed in a free space. Therefore we must give particular considerations to investigate this coherence experimentally. In this paper, a few interesting phenomena related to SGC are summarized, such as gain without inversion, coherent population trapping, phase sensitive spectra, and modifications of absorption, emission, and refraction. We also review the investigations on the realization of SGC, such as modifying the vacuum, coupling levels with static fields, simulating SGC with coherence induced by coherent fields, and studying SGC in special materials.

Cen Jing-sheng

An investigation into lasing without inversion in a Ladder-type three-level atomic system was conducted.With the exhibiting condition of lasing without inversion,the effects of the incoherent pumping and spontaneously generated coherence(SGC) have been studied in detail.The investigation shows that SGC can decrease the phenomena of lasing without inversion(LWI).However,the incoherent pumping can strengthen it.

Jianbing Qi

José Tito Mendonça, Hugo Terças

Shun‐Cai Zhao

A theoretical investigation is carried out into the effect of spontaneously generated coherence (SGC) on the left-handedness in a four-level Y -type atomic system with two highest nearly degenerate lying levels. It is found, with the spontaneously generated coherence intensity enhancing, the atomic system gradually displays left-handedness with simultaneous negative permittivity and permeability. And the refractive index enhances with the increasing intensity of SGC. However, the absorption is suppressed by the SGC effect when the SGC has a large intensity. When the probe field is near-resonant coupled to the atomic system, the appearance of SGC doesn’t always change the permeability from positive to negative and allow for lefthanded behavior, unless the SGC reaches a large intensity.