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Acta Physica Sinica

Ultra-narrow electromagnetically induced transparency and inversionless gain in a ladder-four-level system

Li Yongfang, Sun Jian-feng, 陕西师范大学物理学与信息技术学院,西安〓710062

Published Jan 1, 2003• 2 citations
Publisher

Abstract

In this paper, we study the effects of Rabi frequencies and multi-path radiation on the electromagnetically induced transparency (EIT) and the inversionless gain in a ladder- four-level system driven by two-coherent fields- The Rabi frequencies of the field-driven transition from the upper level to middle levels play an important role for the realization of the ultra-narrow EIT and inversionless gain- Different excitation mechanism can change the position of the EIT- The action of the spontaneous alignment of the dipole moment is investigated- The explanation for the numerical results is presented using the theory of dressed state

DOI
10.7498/aps.52.547

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arXiv:1912.12267•OSA Continuum•Nov 29, 2021•0 citations
In this paper, we study the effects of Rabi frequencies and multi-path radiation on the electromagnetically induced transparency (EIT) and the inversionless gain in a ladder- four-level system driven by two-coherent fields- The Rabi frequencies of the field-driven transition from the upper level to middle levels play an important role for the realization of the ultra-narrow EIT and inversionless gain- Different excitation mechanism can change the position of the EIT- The action of the spontaneous alignment of the dipole moment is investigated- The explanation for the numerical results is presented using the theory of dressed state
Using matrix theory,the absorption and dispersion properties of a lamda-type four-level system driven by two coherent fields are investigated.The result obtained by means of numerical method indicates that by adjusting the intensity of Rabi frequencies of the coherent field in the steady state,double or single electromagnetically induced transparency(EIT) can appear explicitly in this system.And the explanations of these phenomena are given by using the dressed states.In the double electromagnetically induced transparency,the location of transparent windows can be manipulated by controlling the detuning of the driving field.Additionally,it is also found that the medium shows a large refractive index at each transparency window,and the group velocity of the probe laser can be enhanced.
Using density matrix eqution, the absorption and dispersion properties of a A-type four-level system driven by coherent fields are investigated. The result obtained by means of numerical method indicates that by adjusting the intensity of Rabi frequencies of the coherent field in the steady state, three, double or single electromagnetically induced transparency (EIT) can appear explicitly in this system. And the explanations of these phenomena are given by using the dressed states. In the three EIT, the location of transparent windows can be manipulated by controlling the detuning of the driving field. What's more, it is also found that the medium shows a large refractive index at each transparency window, and the group velocity of the probe laser can be enhanced.
Electromagnetically induced transparency(EIT) with extremely narrow spectral width is obtained in a well-studied lambda three level system where a coupling field and a probing field interact with two optical transitions.By tuning coupling field,it excites the transitions between two ground state hyperfine levels and excited state level.In this paper,both EIT and spontaneous radiation induced coherent dip can be obtained,and even the gain is observed to superpose to the EIT window.By discussing the behaviors of probing field absorption profiles under the effect of the tuned coupling field,it can be seen that there are quantum interference and coherence between EIT and spontaneous radiation induced coherent dip,and the coherence becomes remarkable when the excitation frequency of the coupling field satisfies certain conditions.
Atomic coherence and interference play an important role in the study of the atom-photon interactions. Electromagnetically induced transparency (EIT) is an extensively studied two-photon coherence phenomenon theoretically as well as experimentally. EIT is mainly observed in three-level atomic systems which causes transparency by quenching absorption of the medium. In this paper, based on the lambda type three-level system including energy level |1>, |2> and |3>, a microwave driving field is introduced between the excited-state energy level |3> and another excited-state energy level |4> to form an inverted Y-type four-level system. We theoretically study the two- and three-photon coherence in this system. The results show that the coupling field makes the probing absorption intensity at the resonant frequency have a very narrow line-width depression, i.e., EIT. The microwave field causes a dynamic Stark splitting of the energy level |3> and induces the Aulter-Townes double peaks. Their frequency interval is exactly equal to the Rabi frequency of the microwave field. The presence of all three fields induces wide window of EIT at the line center owing to the enhanced depression results. The transient evolution is also discussed to understand the optical switching process in the system. Our theoretical study will be helpful to get a deeper insight into the three-photon effects in multilevel systems.
The absorption properties in an inverted-tripod scheme atomic system driven by the coherent fields are investigated by means of the semiclassical theory.The result obtained by means of numerical method indicates that by adjusting the Rabi frequencies of the coherent fields,there appear triple,double,single electromagnetically induced transparency(EIT).In the triple EIT,the location of transparent windows can be controlled by adjusting the detunings for the coherent fields,and changes continuously,i.e.there exist a series of continuous frequencies for the probe field propagating in an atomic medium without absorption in a certain range.Finally,the explanations of these phenomena are given by using the dressed states.
Electromagnetically induced transparency (EIT) is a well-known phenomenon due in part to its applicability to quantum devices such as quantum memories and quantum gates. EIT is commonly modeled with a three-level lambda system; however, this simplified model does not capture all the physics of EIT experiments with real systems. We present a theoretical study of the effect of two closely-spaced excited states on EIT and off-resonance Raman transitions. In addition to the expected broadening of the EIT resonance and reduction in EIT transparency due to multiple excited states, we find some unexpected and interesting results. A comparison with a model that does not allow for coupling of the excited states shows that the coherent interaction of the fields with two excited states whose separation is smaller than their Doppler broadened linewidth can enhance the EIT transparency under some conditions and can enhance and shift the resonance frequency of off-resonance Raman absorption. Furthermore, through a dressed state analysis of the full four-level system, we find that the underlying mechanism for the reduction in EIT transparency is a shift in the two-photon resonance due to unequal dipole moments of the transitions coupled by the control field. Complete transparency can only be recovered for systems with equal dipole moments or when the separation between the two excited states is at least of the order of the Doppler width. To support our theoretical study, we present experimental EIT measurements in the D1 lines of 85Rb and 87Rb that agree with our predictions of an enhancement or reduction of EIT transparency under specific conditions. The experimental results also verify the roles that the dipole moments and the separation between the two excited states have on recovering the EIT transparency.