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On the Dynamics of the Autler-Townes effect

Arnoldas Seputis

Published Jan 1, 2020• 0 citations
OpenAlex

Abstract

In this thesis the effect of Autler-Townes splitting is revisited and the dynamics of a 2- and 3-level quantum systems, exhibiting this effect, is studied. This effect is a special case of the Stark effect, where the spectral lines of an atom are modified due to an external driving electromagnetic field. Two different articles, describing the Autler-Townes splitting, are studied, where one solves the time-dependent equations of the semi-classical model and the other studies the time-independent Hamiltonian for the system, which is described completely quantum mechanically. In our work, we proceed by employing the semi-classical model but transforming the Hamiltonian into a time-independent form, which makes the model easier to study. Subsequently, we also study the atom as an open quantum system and investigate the effect that the decay of an atom to a vacuum field has on the Autler-Townes splitting. Throughout the thesis, we present the density matrices, and hence the time-evolution of the dynamics, in the Bloch-vector description in an attempt to understand the geometrical nature of the dynamics and, in effect, the Autler-Townes phenomenon.

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Physical Review A•Feb 1, 1998•31 citations
In this thesis the effect of Autler-Townes splitting is revisited and the dynamics of a 2- and 3-level quantum systems, exhibiting this effect, is studied. This effect is a special case of the Stark effect, where the spectral lines of an atom are modified due to an external driving electromagnetic field. Two different articles, describing the Autler-Townes splitting, are studied, where one solves the time-dependent equations of the semi-classical model and the other studies the time-independent Hamiltonian for the system, which is described completely quantum mechanically. In our work, we proceed by employing the semi-classical model but transforming the Hamiltonian into a time-independent form, which makes the model easier to study. Subsequently, we also study the atom as an open quantum system and investigate the effect that the decay of an atom to a vacuum field has on the Autler-Townes splitting. Throughout the thesis, we present the density matrices, and hence the time-evolution of the dynamics, in the Bloch-vector description in an attempt to understand the geometrical nature of the dynamics and, in effect, the Autler-Townes phenomenon.
Understanding the behavior of quantum systems under external perturbations is fundamental in quantum mechanics and has numerous applications in fields such as spectroscopy and quantum computing. In this thesis, we investigate the phenomenon of Autler-Townes doublets in hydrogen atoms numerically, focusing on a three-level model. Autler-Townes doublets arise when a two-level quantum system, such as a hydrogen atom, is subjected to an external electromagnetic field, leading to the splitting of spectral lines due to the Autler-Townes effect. The study involves formulating and solving the population amplitude equations describing the time evolution of the hydrogen atom’s probability amplitudes under the influence of external fields. We employ the Range-Kutta method in MATLAB to numerically solve these equations and analyze the shape and characteristics of Autler-Townes doublets. Our simulations explore the influence of various parameters such as field strength and frequency on the doublet structure. Additionally, our research compares the numerical results obtained from the simulation with the three-level model solutions, providing insights into the dynamic interference and understanding the physical reasons for the modulations in the spectrum. Our findings not only contribute to the understanding of Autler-Townes doublets in hydrogen atoms but also shed light on potential applications in quantum technologies and spectroscopic techniques.
The dynamic Stark effect and Autler-Townes splitting (ATS) are hallmarks of driven two-level systems. We establish a direct correspondence between these quantum phenomena and the parametric normal mode splitting in coupled classical oscillators. This identifies a second-subharmonic ATS under a two-tone parametric drive. We find excellent agreement between the theory and the vibrations of a nanomechanical two-mode system, capturing both the fundamental and second-subharmonic ATS, and allowing quantitative extraction of the modal coupling irrespective of the degree of modal hybridization.
Some features of the optical Autler-Townes effect as observed in Doppler-broadened three-level systems, including the physical significance of the observed line splitting, the conditions for the observation of the doublet, the doublet separation and the detuning effects, are discussed in this paper. A graphical illustration of the phenomenon, based on a search for on-resonance velocity groups, is proposed which allows a complete qualitative discussion of the effect and shows that the observed doublet is not really a splitting of the resonance as for the atom at rest but rather corresponds to a frequency hole where the laser probe does not see any resonant velocity group. The method is applied to real three-level systems of neon as typical cases. A semi-classical density-matrix calculation is performed numerically and definitely confirms the results of the qualitative graphical discussion ; furthermore it shows that, for many experimental situations, the first order approximation is inadequate. The observation of the Autler-Townes doublet in a new experiment using two dye lasers is reported. The experimental results and that of one of our previous experiments are compared with the theoretical predictions ; the agreement is quite satisfactory.
Electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting are two phenomena that could be featured in a variety of three-level atomic systems. The considered phenomena, EIT and AT, are similar ``looking'' in the sense that they are both characterized by a reduction in absorption of a weak field in the presence of a stronger field. In this paper, we explicitly set the threshold of separation between EIT and AT splitting in a unified study of four different three-level atomic systems. Two resonances are studied and compared in each case. A comparison of the magnitudes of the resonances reveals two coupling-field regimes and two categories of three-level system.
In recent years, coherent effects in atomic and molecular systems have been studied extensively, especially in several new classes of effects, such as lasing without inversion (LWI), electromagnetically induced transparency (EIT), coherent population trapping (CPT), AC Stark effect and Autler-Townes (AT) splitting in multilevel systems. The AC stark effect and Autler-Townes splitting in molecules have only been investigated recently. We demonstrate AC stark effect and Autler-Townes (AT) splitting in a lithium molecule using cw multi-photon spectroscopy. The excited upper level of the G1PigG^{1}\\Pi_{g}G1Pig​ is prepared by the optical-optical double resonance (OODR) excitation. The OODR line is split in the presence of a third coupling laser, which couples the upper level to an another intermediate level when the coupling laser is on or near resonance transition. The AT line shape consists of the superposition of ∣MJ∣|M_{J}|∣MJ​∣ components which have been resolved for G1Pig(v=12,J=3,f)G^{1}\\Pi_{g}(v=12, J=3,f)G1Pig​(v=12,J=3,f). We find that the AT splittingis linearly proportional to ∣MJ∣|M_{J}|∣MJ​∣, which allows the excitation of molecules with a selected ∣MJ∣|M_{J}|∣MJ​∣ level. The AC Stark shift of the OODR line is observed when the coupling laser is detuned from the resonance transition.
The probe-field absorption spectra are investigated for three-level atoms interacting with mono- or bichromatic fields in the presence of bath reservoirs of different kinds. Two configurations of atoms with lower-level and upper-level couplings are considered on the basis of Floquet-state dynamics. The multipeak Autler-Townes splitting induced by the resonant interaction of atoms with bichromatic fields is investigated and driving-field effects as well as squeezed-bath effects on the absorption spectra are analyzed. Ultrasharp absorption lines can be obtained in the upper-level coupling scheme due to a mixing of two atomic decay channels by the bichromatic field.