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Journal of Sichuan Normal University

Effect of Vacuum-induced Interference on Probe Absorption and Dispersion of a Λ-type Three-level Atom

Hou Bang

Published Jan 1, 2003• 0 citations
OpenAlex

Abstract

We discuss the effects of the incoherent pumping in both probe and coupling channels on the absorption and dispersion of the probe laser with quantum interference. The incoherent population pumping in the coupling channel decreases the probe transparency. When decay rate in the coupling channel is greater than that in the probe channel, the incoherent population pumping in the probe channel can create the gain without inversion. The probe absorption pattern is upsidedown if the interference is present. When the decay rates in the probe and channels are equal, the incoherent pumping in the probe channel doesn't create the gain until the existence of the interference.

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We discuss the effects of the incoherent pumping in both probe and coupling channels on the absorption and dispersion of the probe laser with quantum interference. The incoherent population pumping in the coupling channel decreases the probe transparency. When decay rate in the coupling channel is greater than that in the probe channel, the incoherent population pumping in the probe channel can create the gain without inversion. The probe absorption pattern is upsidedown if the interference is present. When the decay rates in the probe and channels are equal, the incoherent pumping in the probe channel doesn't create the gain until the existence of the interference.
We have analyzed the properties of weak probe absorption in a closed four-level Y -type system driven by a coherent driving field. The system with two nearly degenerate uppermost levels interacting with the same modes of the vacuum radiation field exhibits the interference effect between the spontaneous decay channels. The phenomenon of this quantum interference can significantly change the absorptive response of the weak probe field. On varying the amplitude of the resonant driving field, in the absence of incoherent pumping in the upper transitions the system can display probe transparency as well as enhanced absorption peak under the condition of resonant detuning of the probe field. With the application of incoherent pumping to the system the phenomenon of symmetric light amplification with two distinct gain peaks one each at the positions of Autler–Townes resonances can be achieved in the presence of the decay-interference effect. We have also shown that the unidirectional incoherent pumping mode is necessary for the evolution of probe gain.
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.
The gain, absorption and dispersion properties of a probe field for a four level N-type atomic system with a normal vacuum and a squeezed vacuum fields is studied. Under such conditions that normal and squeezed vacuum-induced interference among decay channels is significant. Our study also reveals that the quantum interference will produce a remarkable effect on the absorption and dispersion properties of the system. A single squeezed vacuum is coupled to three transitions. Numerically the effect of the squeezing vacuum field parameters and the relative phases between the squeezed vacuum and the probe (strong) fields on the index of refraction is analyzed.
In a three-level V-type atomic system without any external coherent driving, owing to the coherence that results from the vacuum of the radiation field, both the probe gain with and without population inversion can be achieved with very weak incoherent pumping. The gain is achieved in the absence of any external coherent driving field, so it is different from the gain without inversion in ordinary laser-driven schemes where a coherent driving field is necessary to create the coherence. The gain is also different from the conventional lasing gain because the population inversion is achieved via vacuum-induced coherence, which is dependent on the atomic coherence.
The dynamical behaviour of the dispersion and the absorption in a nearly equispaced ladder-type three-level atomic system is investigated. It is shown that in the presence of decay-induced interference the probe dispersion and absorption are phase dependent. The required switching times for switching the group velocity of a probe field from subluminal to superluminal pulse propagation is then discussed. We find that applying an incoherent pumping field provides an additional control parameter for switching the probe absorption to probe gain.
When the interactions of the two coupling transitions from an excited level to two nearly degenerate ground levels with the same vacuum occur in a four-level tripod-scheme atomic system, vacuum-induced coherence (VIC) results from the quantum interference between the two spontaneous transitions. We investigate the effects of VIC and the relative phase between the two coupling fields on the probe absorption and dispersion properties as well as the group velocity of the probe field. We find that by adjusting the incoherent pumping field and VIC as well as the relative phase, the central absorption peak in the double transparency spectrum reduces, even develops into a gain dip, and the probe field propagates at a velocity from superluminal to subluminal. It is particularly pointed out that the subluminal light propagation with gain without inversion can be realized in such a system. The physical interpretation of the phenomena has been given.