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Laser & Photonics Review

Fundamental Distinction of Electromagnetically Induced Transparency and Autler–Townes Splitting in Breaking the Time‐Reversal Symmetry

Haodong Wu, Ya-Ping Ruan, Zhixiang Li, Ming‐Xin Dong, Miao Cai, Jiang-Shan Tang, Lei Tang, Han Zhang, Min Xiao, Keyu Xia

Published Jul 3, 2022• 49 citations

Abstract

Abstract Despite the essential difference in underlying physics, electromagnetically induced transparency (EIT) and Autler–Townes splitting (ATS) are difficult to be discriminated because they cause resemble absorption and dispersion to a probe electromagnetic field. They are mainly discerned in the sense of absorption profile fitting. Here, the breakdown of the time‐reversal symmetry (TRS), namely optical nonreciprocity in the EIT and ATS configurations are experimentally observed by using warm rubidium atoms. The microscopic Doppler effect due to atomic thermal motion causes strong optical nonreciprocity to the probe field in the EIT configuration. In stark contrast, the propagation of the probe field is primarily reciprocal in the ATS configuration. The experimental observations in this study objectively distinguish the EIT and ATS effects in the fundamental physics of breaking the TRS. This experiment proves a concept of using the TRS as a testbed for discerning fundamental physical effects.

DOI: 10.1002/lpor.202100708

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Scientific Reports•Jan 11, 2016•21 citations

Abstract Despite the essential difference in underlying physics, electromagnetically induced transparency (EIT) and Autler–Townes splitting (ATS) are difficult to be discriminated because they cause resemble absorption and dispersion to a probe electromagnetic field. They are mainly discerned in the sense of absorption profile fitting. Here, the breakdown of the time‐reversal symmetry (TRS), namely optical nonreciprocity in the EIT and ATS configurations are experimentally observed by using warm rubidium atoms. The microscopic Doppler effect due to atomic thermal motion causes strong optical nonreciprocity to the probe field in the EIT configuration. In stark contrast, the propagation of the probe field is primarily reciprocal in the ATS configuration. The experimental observations in this study objectively distinguish the EIT and ATS effects in the fundamental physics of breaking the TRS. This experiment proves a concept of using the TRS as a testbed for discerning fundamental physical effects.

Autler-Townes splitting (ATS) and electromagnetically-induced transparency (EIT) both yield transparency in an absorption profile, but only EIT yields strong transparency for a weak pump field due to Fano interference. Empirically discriminating EIT from ATS is important but so far has been subjective. We introduce an objective method, based on Akaike's information criterion, to test ATS vs. EIT from experimental data and determine which pertains. We apply our method to a recently reported induced-transparency experiment in superconducting circuit quantum electrodynamics.

Autler-Townes splitting (ATS) and electromagnetically induced transparency (EIT) both yield transparency in an absorption profile, but only EIT yields strong transparency for a weak pump field due to Fano interference. Empirically discriminating EIT from ATS is important but so far has been subjective. We introduce an objective method, based on Akaike's information criterion, to test ATS vs EIT from experimental data for three-level atomic systems and determine which pertains. We apply our method to a recently reported induced-transparency experiment in superconducting-circuit quantum electrodynamics.

Electromagnetically induced transparency (EIT) and Autler–Townes splitting (ATS) are two similar yet distinct phenomena that modify the transmission of a weak probe field through an absorption medium in the presence of a coupling field, featured in a variety of three-level atomic systems. In many applications it is important to distinguish EIT from ATS splitting. We present EIT and ATS spectra in a three-level cascade system, involving cold cesium atoms in the Rydberg state. The EIT linewidth, γ EIT , defined as the full width at half maximum of the transparency window, and the ATS splitting, γ ATS , defined as the peak-to-peak distance between AT absorption peaks, are used to delineate the EIT and ATS regimes and to characterize the transition between the regimes. In the cold-atom medium, in the weak-coupler (EIT) regime γ EIT ≈ A + B ( + , where Ω c and Ω p are the coupler and probe Rabi frequencies, Γ eg is the spontaneous decay rate of the intermediate 6P 3/2 level, and parameters A and B that depend on the laser linewidth. We explore the transition into the strong-coupler (ATS) regime, which is characterized by the relation γ ATS ≈ Ω c . The experiments are in agreement with numerical solutions of the Master equation. Our analysis accounts for non-ideal conditions that exist in typical realizations of Rydberg-EIT, including laser-frequency jitter, Doppler mismatch of the utilized two-color Rydberg EIT system, and strong probe fields. The obtained criteria to distinguish cold-atom EIT from ATS are readily accessible and applicable in practical implementations.

In this work, we report on experimentally discerning Autler–Townes splitting (ATS) from electromagnetically induced transparency (EIT). Our findings are based on a Ξ (ladder) transition 5S1/2→5P3/2→5D5/2 of 87Rb atoms under different laser detuning combinations. Based on the ratio of power levels of two individual and counter-propagating lasers through a room temperature Rb vapor cell, we experiment on two different categories of Ξ configuration: types I and II. For type I, 5P3/2→5D5/2 transition is strongly driven, and we observe EIT. Type II (5S1/2→5P3/2 strongly coupled) exhibits pure ATS. Under two different two-photon detuning conditions, ATS and EIT are studied. While ATS becomes stronger near exact two-photon resonance condition, the EIT weakens. This is supported by the analysis of blue light emanating from 5D5/2→6P3/2→5S1/2 decay. The complete opposite behavior of these two phenomena at exact two-photon resonance condition can be used to clearly discern EIT from ATS.