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Communications in Theoretical Physics

Effects of Spontaneously Generated Coherence on Intensity-Intensity Correlation in a Driven Y-Type Atom

Fei Wang, Wen-Xing Shi, Cheng Gong

Published Dec 1, 2011• 6 citations
Publisher

Abstract

In this paper, we investigate the spontaneously generated coherence (SGC) effects on the fluorescence fields intensity-intensity correlation in a resonant driven four-level Y-type atomic system. By using a strong control field, in the absense of SGC effects, strong correlation and anticorrelation fluorescence photons can be produced from two ladder transitions in this system respectively. However, in the presence of SGC effects, the fluorescence fields correlation properties are reversed for the two transitions. The above phenomena can be traced to the quantum destructive or constructive interference in terms of dressed states.

DOI
10.1088/0253-6102/56/6/19

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In this paper, we investigate the spontaneously generated coherence (SGC) effects on the fluorescence fields intensity-intensity correlation in a resonant driven four-level Y-type atomic system. By using a strong control field, in the absense of SGC effects, strong correlation and anticorrelation fluorescence photons can be produced from two ladder transitions in this system respectively. However, in the presence of SGC effects, the fluorescence fields correlation properties are reversed for the two transitions. The above phenomena can be traced to the quantum destructive or constructive interference in terms of dressed states.
The fluorescence photon correlations in a driven four-level atom consisting of three upper closely lying excited states and a single lower state are investigated. It is found that in the presence of triple spontaneously generated coherence (SGC) effects, which are created by three degenerate levels coupling to the common ground state via the same vacuum mode, the correlation properties of the three fluorescence fields can be switched from strong correlation to anticorrelation or vice versa by modifying the detunings. In addition, such a system is very sensitive to the relative phases of the three fields, which can provide an effective way to control the photon correlation. Physically, these interesting phenomena can be interpreted in terms of dressed state analysis.
The resonance fluorescence spectra of a laser-driven four-level closed-loop diamond-shape atomic system are investigated in this paper. The four decay channels in the system interfere with each other in different ways according to several distinct arrangements of the two intermediate atomic levels, and hence produce the spontaneously generated coherence (SGC) effects. The numerical calculation shows that the amplitude, the linewidth and the number of sidebands of the resonance fluorescence spectrum are deeply modified by the SGC effects; accordingly, interesting effects such as the spectral-line narrowing, spectral-line suppression, spectral-line enhancement and even the complete quenching of fluorescence are generated under certain conditions. Moreover, we propose a new kind of level structure, the seesaw structure, in which the SGC effect can also be attained without the rigorous conditions of degenerate levels. In the end, we discuss the possibility of demonstrating our scheme in real atomic systems and summarize our results.
The effect of spontaneously generated coherence (SGC) on spontaneous emission and dynamical evolution of a microwave-driven four-level atomic system is studied. Interesting phenomena due to SGC, such as spectral-line narrowing, spectra-line enhancement, spectral-line suppression, and fluorescence quenching, are shown in the spontaneous emission spectra, which can be effectively modulated by amplitude and phase of the microwave field. Due to SGC, the total populations are partly, even completely, trapped in upper levels in steady state, the decay time of which is sensitive to the phase of the microwave field. In the dressed state picture, multiple SGC arise during the process of three close-lying states decaying to the same state. The corresponding experiment to observe the expected phenomena related to SGC can be more conveniently realized in atoms, since no rigorous conditions are required and the amplitude and phase of the microwave field can be conveniently controlled.
This paper investigates the effects of spontaneously generated coherence(SGC) on the probe absorption in the Y-type four-level atomic system driven by three fields.It finds that the probe absorption at the resonance center shows the different phenomena with the SGC effects.When SGC produces the destructive interference on the probe absorption,the absorption at the resonance center is reduced with the SGC enhancement and the gain appears there.When SGC produces the constructive interference on the probe absorption,the absorption at the resonance center is enhanced with the SGC enhancement.That is electromagnetically induced absorption(being abbreviated EIA);the intensity of double electromagnetically induced transparency(being abbreviated EIT);at both sides of the resonance is increased,and the windows get wider.At the same time,the linewidth of the absorption at the resonance center becomes narrow and the transparent windows at both sides of the resonance get wider when the spontaneous decay rate of energy levels |3〉→|2〉 and 4〉→|2〉 is decreased at the ratio of the spontaneous decay rate of energy levels |3〉→|2〉 and |4〉→|2〉 being constant.
We examine the intensity correlation functions of the two fluorescent fields that are emitted from the top and middle states of a doubly driven three-level atom in the cascade configuration. Novel interference effects are shown. (i) Both of the fluorescent fields have anticorrelations which can exist for long times when the applied fields are on the two-photon resonance and far off one-photon resonances. (ii) Both of the fluorescent fields have strong correlations when the applied fields are far off one- and two-photon resonances. In particular, the extremely strong correlation occurs for the photons emitted from the top state. The above phenomena are traced to the multiple interference mechanisms.
We show that strongly correlated and anticorrelated photons can be produced from two fluorescent fields emitted by a driven cascade atom with split metastable states. Depending on the choice of parameters, we have strong correlations for both fluorescent fields, anticorrelations for both, and strong correlation for one and anticorrelation for the other. In the presence of level splitting, we have two interfering cascade-dressed transitions from the top state to the antisymmetric superposition of the metastable states. The interference between the two cascade-dressed transitions is responsible for the strong correlations and anticorrelations.