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Optics Letters

Long-scale decoherence and recoherence of partially coherent light in a graded-index waveguide

Nikolai I. Petrov

Published Sep 9, 2025• 1 citation
Publisher

Abstract

The nonparaxial propagation of partially coherent Gaussian Schell-model (GSM) beams in a graded-index waveguide is studied using the coherent states and coherent modes decomposition methods, as well as perturbation theory. Long-scale decoherence and recoherence of the GSM beam occur due to the revival effect caused by mode interference. It is shown that the radius of coherence and the degree of coherence can be determined based on measurements of purely geometric characteristics of the GSM beam. The information entropy and quantum mechanical purity of GSM beams are evaluated.

DOI
10.1364/ol.571081

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The nonparaxial propagation of partially coherent Gaussian Schell-model (GSM) beams in a graded-index waveguide is studied using the coherent states and coherent modes decomposition methods, as well as perturbation theory. Long-scale decoherence and recoherence of the GSM beam occur due to the revival effect caused by mode interference. It is shown that the radius of coherence and the degree of coherence can be determined based on measurements of purely geometric characteristics of the GSM beam. The information entropy and quantum mechanical purity of GSM beams are evaluated.
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Analytical expression is obtained for the cross-spectral density function of a Gaussian Schell-model (GSM) beam passing through an electromagnetic induced transparency (EIT) atomic vapor. The formula can be used in the study of the changes in the spectral density and spectral degree of coherence of the beam through the EIT atomic vapor. Numerical examples show that both the spectral density and the spectral degree of coherence of the GSM beam can be modulated by the Rabi frequency of the control light.
The role of spatial coherence on diffraction intensity is investigated for a partially coherent incident Gaussian Schell-model beam which is diffracted from a two-level atomic grating. It is shown that the performance of the atomic grating is greatly influenced by the spectral coherence width of the partially coherent fields. It is observed that relatively large intensity of the diffracted light can be obtained via spatial coherence, beam width, interaction length, and mode index of partially coherent incident light. The scheme provides possibilities for the potential applications of atomic grating in lensless imaging using the partially coherent light field.
The quantum theory of the electromagnetic field uncovered that classical forms of light were indeed produced by distinct superpositions of nonclassical multiphoton wave packets. This situation prevails for partially coherent light, the most common kind of classical light. Here, for the first time, to our knowledge, we demonstrate the extraction of the constituent multiphoton quantum systems of a partially coherent light field. We shift from the realm of classical optics to the domain of quantum optics via a quantum representation of partially coherent light using its complex-Gaussian statistical properties. Our formulation of the quantum Gaussian-Schell model (GSM) unveils the possibility of performing photon-number-resolving (PNR) detection to isolate the constituent quantum multiphoton wave packets of a classical light field. We experimentally verified the coherence properties of isolated vacuum systems and wave packets with up to 16 photons. Our findings not only demonstrate the possibility of observing quantum properties of classical macroscopic objects but also establish a fundamental bridge between the classical and quantum worlds.
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Pure states are usually used to observe quantum phenomena. In this study, we show that a quantum superposition of spatially displaced mixed cat states can be generated within an optical waveguide via nonparaxial unitary evolution of the initial low coherence (low purity) light beam. It is shown that highly mixed Schrodinger cat states can be observed at a well-defined propagation distance. The importance of the long-term decoherence and recoherence of the original wave packet in observing the mixed cat states is demonstrated. The Heisenberg and Schrodinger-Robertson uncertainty relations for mixed cat states are evaluated. We have demonstrated the feasibility of our method using accurate numerical simulations for the parameters of the source and optical waveguide available in practice.