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Chinese Physics B

Observation of linewidth narrowing due to a spontaneously generated coherence effect

Si-Cong Tian, Chun-Liang Wang, Zhi‐Hui Kang, Xiu-Bin Yang, Ren-Gang Wan, Xiaojun Zhang, Hang Zhang, Yun Jiang, Haining Cui, Jin-Yue Gao

Published Jun 1, 2012• 4 citations
Publisher

Abstract

We investigate the resonance fluorescence spectrum of an atomic three-level ladder system driven by two laser fields. We show that such a system emulates to a large degree a V-type atom with parallel dipole moments-the latter being a system that exhibits spontaneously generated coherence and can display ultrasharp spectral lines. We find a suitable energy scheme in a 85 Rb atom and experimentally observe the narrowing of the central peak in a rubidium atomic beam. The corresponding spectrum can convincingly demonstrate the existence of spontaneously generated coherence.

DOI
10.1088/1674-1056/21/6/064206

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We investigate the resonance fluorescence spectrum of an atomic three-level ladder system driven by two laser fields. We show that such a system emulates to a large degree a V-type atom with parallel dipole moments-the latter being a system that exhibits spontaneously generated coherence and can display ultrasharp spectral lines. We find a suitable energy scheme in a 85 Rb atom and experimentally observe the narrowing of the central peak in a rubidium atomic beam. The corresponding spectrum can convincingly demonstrate the existence of spontaneously generated coherence.
We investigate the resonance fluorescence spectrum of an atomic three-level ladder system driven by two laser fields.We show that such a system emulates to a large degree a V-type atom with parallel dipole moments-the latter being a system that exhibits spontaneously generated coherence and can display ultrasharp spectral lines.We find a suitable energy scheme in a 85Rb atom and experimentally observe the narrowing of the central peak in a rubidium atomic beam.The corresponding spectrum can convincingly demonstrate the existence of spontaneously generated coherence.
We experimentally study the resonance fluorescence from an excited two-level atom when the atomic upper level is coupled by a nonresonant field to a higher-lying state in a rubidium atomic beam. The heights, widths and positions of the fluorescence peaks can be controlled by modifying the detuning of the auxiliary field. We explain the observed spectrum with the transition properties of the dressed states generated by the coupling of the two laser fields. We also attribute the line narrowing to the effects of Spontaneously Generated Coherence between the close-lying levels in the dressed state picture generated by the auxiliary field. And the corresponding spectrum can be viewed as the evidence of Spontaneously Generated Coherence. The experimental results agree well with calculations based on the density-matrix equations.
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.
This paper investigates the effects of spontaneously induced coherence on absorption properties in a nearly equispaced three-level ladder-type system driven by two coherent fields. It find that the absorption properties of this system with the probe field applied on the lower transition can be significantly modified if this coherence is optimized. In the case of small spontaneous decay rate in the upper excited state, it finds that such coherence does not destroy the electromagnetically induced transparency (EIT). Nevertheless, the absorption peak on both sides of zero detuning and the linewidth of absorption line become larger and narrower than those in the case corresponding to the effects of spontaneously induced coherence; while in the case of large decay rate, it finds that, instead of EIT with low resonant absorption, a sharp absorption peak at resonance appears. That is, electromagnetically induced absorption in the nearly equispaced ladder-type system can occur due to such coherent effects.
It is shown that simultaneous narrowing occurs upon the central peak and outer sidebands in the resonance fluorescence spectrum by simulating vacuum-induced quantum interference in a Λ-type three-level atomic system, where the transition dipole moments are orthogonal, the metastable states are coupled to each other via a microwave field and a laser field is applied to one dipole-allowed atomic transition. With the decrease in the ratio of the laser Rabi frequency to the microwave Rabi frequency, the fluorescence spectrum eventually reverts to an ultrasharp triplet. The physical interpretation of the spectral characteristics is given in terms of dressed states.