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Acta Physica Sinica

Effect of vacuum-induced coherence in a four-level atomic system via quantum interference

Jun Chen, Liu Zheng-Dong, Zheng Jun, Fang Hui-Juan, (1)南昌大学近代物理研究所,南昌 330031; (2)南昌大学近代物理研究所,南昌 330031;广东工业大学实验中心,广州 510090; (3)南昌大学近代物理研究所,南昌 330031;南昌大学纳米技术工程研究中心,南昌 330047; (4)南昌大学纳米技术工程研究中心,南昌 330047

Published Jan 1, 2007• 4 citations
Publisher

Abstract

In this paper,we report the effects of vacuum-induced coherence in a laser-driven four-level atom consisting of three near-degenerate upper levels having an additional coherence term due to interaction with the vacuum of the radiation field. We show that such coherence preserves the electromagnetically induced transparency and optical bistability phenomena. The dynamical behavior of the population distribution via vacuum-induced coherence was also analyzed numerically.

DOI
10.7498/aps.56.6441

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In this paper,we report the effects of vacuum-induced coherence in a laser-driven four-level atom consisting of three near-degenerate upper levels having an additional coherence term due to interaction with the vacuum of the radiation field. We show that such coherence preserves the electromagnetically induced transparency and optical bistability phenomena. The dynamical behavior of the population distribution via vacuum-induced coherence was also analyzed numerically.
When a four-level Y\mathsf{Y}Y-type atom with two highest nearly degenerate lying levels interacts with the same vacuum radiation field, its excited levels have vacuum-induced coherence due to the quantum interference between the spontaneous decay channels. We consider the effects of the vacuum-induced coherence on the electromagnetically induced transparency against single- and two-photon absorption in the atomic system. We find that the vacuum-induced coherence can lead to probe gain without incoherent pumping. On the other hand, the coherence can suppress the two-photon transparency, even in some cases where it can enhance the two-photon absorption. Another important result is the finding of the crucial role played by the relative phase between the probe and coupling fields: the two-photon transparency and the probe gain spectra can be modulated by this phase.
Due to interaction with the vacuum of the radiation field, a K-type atomic system with near-degenerate excited and ground levels, which is driven by two strong coherent fields and two weak probe fields, has additional coherence terms — the vacuum-induced coherence (VIC) terms. In this paper, we find that, if the interference is optimized, the two-photon absorption properties of this atom system can be significantly modified and electromagnetically-induced transparency (EIT) is dependent on this interference. Furthermore, we find that in all the cases the coherence can suppress or enhance the partial two-photon transparency, while the complete transparency window is still strictly preserved, which means that it cannot be affected by the VIC. Another important result is the finding of the crucial role played by the relative phase between the probe and coupling fields: the relative height of absorption peaks can be modulated by the relative phase. The physical interpretation of the phenomena has been given.
In this paper we investigate the resonance fluorescence, the squeezing, and the absorption spectra of a laser-driven four-level atom consisting of three closely spaced upper levels decaying to a common lower level. The three upper levels are coupled by the same vacuum modes to the lower level leading to spontaneously generated coherence effects. High population inversion and extremely narrow emission lines are obtained with moderate Rabi frequencies, which are a direct consequence of decay-induced interferences. The fluorescent field is shown to exhibit two-mode squeezing in the in-phase quadrature. Squeezing in both quadratures simultaneously at different frequencies is greatly enhanced when quantum interference is accounted for. We also examine the absorption spectrum of a weak field and demonstrate that quantum interference can induce two prominent and nearly transparent holes where the slope of the refractive index is very steep. This special situation could allow the simultaneous propagation of two weak pulses with different frequencies, which could be feasibly exploited towards the realization of the entanglement of two photons.
Quantum interference and coherence effects in the interaction of atoms with the quantized electromagnetic field are investigated theoretically. A general master equation for the description of atom-field interactions is introduced. The interplay of the concepts of complementarity and interference in the time-energy domain are studied on the basis of the fluorescence light emitted by a single laser-driven atom, where the coherence of spontaneous processes gives rise to quantum interference in the spectrum of resonance fluorescence. The vacuum-induced dipole-dipole interaction in pairs of multi-level atoms is analyzed. It is shown that the interaction between orthogonal transition dipole moments of different atoms does not only influence the system dynamics crucially, but implies that the few-level approximation in general cannot be applied to near-degenerate Zeeman sublevels of the atomic level scheme. Potential applications of dipole-dipole interacting multi-level atoms for the implementation of decoherence-free subspaces and the generation of entanglement between atomic states are examined. The generation of an entangled state of the radiation field with a macroscopic number of photons is discussed on the basis of a single-atom laser.
When the transitions connected by two nearly degenerate ground levels with an intermediate level in a four-level inverted Y-type atom interact with the same vacuum radiation field,which will lead to the quantum interference and create the vacuum-induced coherence.We find that the vacuuminduced coherence can suppress the single-and two-photon transparency at resonance and lead to single-photon probe gain at other frequency.Meanwhile,it is shown that the single-and two-photon absorption spectra can be drastically modulated by the relative phase between the probe and coupling fields.