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Physica Scripta

Fano-like interference induced modification of Autler-Townes doublet spectrum via phase-dependent superposition of atomic states

Bibhas Kumar Dutta, Pradipta Panchadhyayee

Published Jul 28, 2020• 0 citations
Publisher

Abstract

Abstract A four-level atomic model is proposed to exhibit the evolution of Fano-like interference effect in the spontaneous emission spectrum of Autler-Townes (AT) doublet when the atom is initially prepared in the phase-dependent superposition of quantum states. By using this model, phase-dependent generation of a narrow spectral line within the AT-doublet is predicted. This feature is shown to be modified by the AT-peak-splitting effect. In addition, it has been also shown that the latter may be accompanied by an anomalous peak shifting effect, which is found to be obtained in a typical phase-coherent atomic ensemble or phaseonium under consideration. As a whole, the emission spectrum can be obtained with three peaks instead of two peaks associated with a sharp spectral hole as a consequence of the emergence of asymmetric Fano-like resonance. This is the most interesting outcome of the present study.

DOI
10.1088/1402-4896/abaa08

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Abstract A four-level atomic model is proposed to exhibit the evolution of Fano-like interference effect in the spontaneous emission spectrum of Autler-Townes (AT) doublet when the atom is initially prepared in the phase-dependent superposition of quantum states. By using this model, phase-dependent generation of a narrow spectral line within the AT-doublet is predicted. This feature is shown to be modified by the AT-peak-splitting effect. In addition, it has been also shown that the latter may be accompanied by an anomalous peak shifting effect, which is found to be obtained in a typical phase-coherent atomic ensemble or phaseonium under consideration. As a whole, the emission spectrum can be obtained with three peaks instead of two peaks associated with a sharp spectral hole as a consequence of the emergence of asymmetric Fano-like resonance. This is the most interesting outcome of the present study.
Abstract It has been shown that coherence effects have a marked influence in the spontaneous emission spectrum of a three-level Λ -type atom driven by weak coherent and incoherent fields. Phase dependent evolution of interference effects leading to spectral narrowing, generation of spectral hole and dark line are exhibited in the present scheme when the atom does not interact with the incoherent fields. The basic mechanism underlying this scheme seems to be appropriate for a phaseonium. Apart from phase-coherence introduced in the system the phenomenon of line narrowing, in the presence of weak incoherent pumping, can be achieved in a different way as a consequence of two competitive resonant effects: sharp non-Lorentzian and symmetric Fano-like-resonance contributions to the line shape. In both the situations, the evolution of narrow structures in the line shape can be achieved even when the emission is influenced by the dephasing of Raman coherence.
Transient four-wave mixing (FWM) spectra from excitonic Fano resonance (FR) states in biased superlattices are theoretically investigated by numerically solving the semiconductor Bloch equations adopting FR wave functions of the excitonic Wannier-Stark ladder as an expansion basis set. It is found that an Aulter-Townes-like doublet arises from resonant excitation of FR excitons, and shows conspicuous asymmetry in spectrally resolved FWM signals, the degree of which depends strongly upon a Fano-qqq parameter. Furthermore, the many-body Coulomb exchange effects markedly modify the spectral profiles, so that either lobe of the doublet is considerably narrowed with accompanying reversal of the asymmetry pattern. The effects also shift the overall resonance spectra toward the high-energy side. The three findings of spectral narrowing, asymmetry reversal, and blue shift feature the present dressed FR system. The corresponding time-resolved spectra are also discussed from the viewpoint of the Rabi oscillation.
Abstract This study shows atomic dephasing and coherence controlled tuning of a triple color scattering light from a four-level atomic system into the ones of single and double color when the system is cyclically coupled with one microwave field and two optical fields. The scattering light with the symmetric double resonance in the latter case tunes into two distinct features of the asymmetric Fano-like resonance using relative phase of the coupling fields and vice versa. The asymmetric resonance, in each case, agrees excellently with the original formulation of Fano (1961 Phys. Rev . 124 1866). The coherence tuning of the resonances, caused by the constructive interference effect in the spectrum, is analyzed analytically. Distinct in the technique, we further show atomic dephasing-induced tuning of the symmetric double and asymmetric single Fano-like resonance into a Lorentzian like statistical behavior. Upon adjusting the relative amplitude of the coupling fields in favor of the resonance tuning, the triple color scattered light is controlled from a sharpened central single and broadened sides double line through central broadened single and sides sharpened double line.
The modification of the spontaneous emission spectrum has been studied in this paper in a four-level doubly driven N-type atomic system. In the presence of two coherent fields, emphasis has been given to studying the spectral distribution of spontaneous emission in the relaxation process of the initially prepared excited level. The phenomenon of quantum interference dynamically induced in the system by these fields can significantly change the spontaneous emission spectrum. We have shown the emergence of a two-peak spectrum where two widely separated symmetric peaks are associated with a sharp dark line at their mid-position. At different dynamic conditions, we have also shown that two symmetric peaks may appear in the spectrum with an extended dark zone between them. Depending on the values of the Rabi frequencies and the detunings of the external fields, one can achieve a large enhancement of very narrow spectral components within the spontaneous emission line shape under different conditions. The phenomenon of suppression of spectral line and the selective cancellation of spontaneous emission have also been discussed. The results shown in various cases are analysed by considering all possible dressed states corresponding to the bare state model. The influence of collision-induced effects on the spontaneous emission spectrum is investigated as a conditional case.
We present a bound-continuum ionization model combined with numerical simulations to investigate the asymmetric features of Autler-Townes (AT) splitting in the ionization spectra of hydrogen atoms, induced by a spectrally phase-modulated ultrashort pulse. This model incorporates a resonance-enhanced two-photon ionization process, enabling transitions from the ground electronic state to the continuum state via the first excited electronic state through the absorption of two photons. By comparing our model predictions with exact numerical simulations based on time-dependent electronic wave-packet calculations, we demonstrate that the characteristics of the AT doublets, shaped by the spectral phase, emerge from the competing effects of selective population of dressed states and the transition amplitude to the continuum. In addition, through a perturbative analysis of the photoelectronic spectrum and the application of the Magnus expansion, we reveal a correlation between the number of AT fringes, resonant states, and pulse area, while drawing insights from bound states. This work enhances our understanding of how the spectral phase can be utilized to explore bound-state effects in ultrafast ionization dynamics.
The effects of Doppler broadening on Autler-Townes (AT) splitting in six-wave mixing (SWM) are investigated by the dressed-state model. We analyze the velocities at which the atoms are in resonance with the dressed states through Doppler frequency shifting and find that, depending on the wave-number ratio, there may be two resonant velocities which can originate from resonance with one of the dressed states or from resonance with two different dressed states. Based on this model, we discuss a novel type of AT doublet in the SWM spectrum, where macroscopic effects play an important role. Specifically, the existence of resonant peaks requires polarization interference between atoms of different velocities in addition to a change in the number of resonant atoms involved. Our model can also be employed to analyze electromagnetically induced transparency resonance and other types of Doppler-free high-resolution AT spectroscopy.