Maximum Refractive Index of an Atomic Medium

Maximum Refractive Index of an Atomic Medium

It is interesting to observe that all optical materials with a positive refractive index have a value of index that is of order unity. Surprisingly, though, a deep understanding of the mechanisms that lead to this universal behavior seems to be lacking. Moreover, this observation is difficult to rec...

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Autores principales: Francesco Andreoli, Michael J. Gullans, Alexander A. High, Antoine Browaeys, Darrick E. Chang
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Lenguaje:EN
Publicado: American Physical Society 2021
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QC1-999
Acceso en línea:https://doaj.org/article/8d2183f95ec443508cf08c3d890fbadd
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spelling oai:doaj.org-article:8d2183f95ec443508cf08c3d890fbadd2021-12-02T14:36:20ZMaximum Refractive Index of an Atomic Medium10.1103/PhysRevX.11.0110262160-3308https://doaj.org/article/8d2183f95ec443508cf08c3d890fbadd2021-02-01T00:00:00Zhttp://doi.org/10.1103/PhysRevX.11.011026http://doi.org/10.1103/PhysRevX.11.011026https://doaj.org/toc/2160-3308It is interesting to observe that all optical materials with a positive refractive index have a value of index that is of order unity. Surprisingly, though, a deep understanding of the mechanisms that lead to this universal behavior seems to be lacking. Moreover, this observation is difficult to reconcile with the fact that a single isolated atom is known to have a giant optical response, as characterized by a resonant scattering cross section that far exceeds its physical size. Here, we theoretically and numerically investigate the evolution of the optical properties of an ensemble of ideal atoms as a function of density, starting from the dilute gas limit, including the effects of multiple scattering and near-field interactions. Interestingly, despite the giant response of an isolated atom, we find that the maximum index does not indefinitely grow with increasing density but rather reaches a limiting value of n≈1.7. This limit arises purely from electrodynamics, as it occurs at densities far below those where chemical processes become important. We propose an explanation based upon strong-disorder renormalization group theory, in which the near-field interaction combined with random atomic positions results in an inhomogeneous broadening of atomic resonance frequencies. This mechanism ensures that, regardless of the physical atomic density, light at any given frequency only interacts with at most a few near-resonant atoms per cubic wavelength, thus limiting the maximum index attainable. Our work is a promising first step to understand the limits of the refractive index from a bottom-up, atomic physics perspective, and it also introduces the renormalization group as a powerful tool to understand the generally complex problem of multiple scattering of light overall.Francesco AndreoliMichael J. GullansAlexander A. HighAntoine BrowaeysDarrick E. ChangAmerican Physical SocietyarticlePhysicsQC1-999ENPhysical Review X, Vol 11, Iss 1, p 011026 (2021)
institution DOAJ
collection DOAJ
language EN
topic Physics
QC1-999
spellingShingle Physics
QC1-999
Francesco Andreoli
Michael J. Gullans
Alexander A. High
Antoine Browaeys
Darrick E. Chang
Maximum Refractive Index of an Atomic Medium
description It is interesting to observe that all optical materials with a positive refractive index have a value of index that is of order unity. Surprisingly, though, a deep understanding of the mechanisms that lead to this universal behavior seems to be lacking. Moreover, this observation is difficult to reconcile with the fact that a single isolated atom is known to have a giant optical response, as characterized by a resonant scattering cross section that far exceeds its physical size. Here, we theoretically and numerically investigate the evolution of the optical properties of an ensemble of ideal atoms as a function of density, starting from the dilute gas limit, including the effects of multiple scattering and near-field interactions. Interestingly, despite the giant response of an isolated atom, we find that the maximum index does not indefinitely grow with increasing density but rather reaches a limiting value of n≈1.7. This limit arises purely from electrodynamics, as it occurs at densities far below those where chemical processes become important. We propose an explanation based upon strong-disorder renormalization group theory, in which the near-field interaction combined with random atomic positions results in an inhomogeneous broadening of atomic resonance frequencies. This mechanism ensures that, regardless of the physical atomic density, light at any given frequency only interacts with at most a few near-resonant atoms per cubic wavelength, thus limiting the maximum index attainable. Our work is a promising first step to understand the limits of the refractive index from a bottom-up, atomic physics perspective, and it also introduces the renormalization group as a powerful tool to understand the generally complex problem of multiple scattering of light overall.
format article
author Francesco Andreoli
Michael J. Gullans
Alexander A. High
Antoine Browaeys
Darrick E. Chang
author_facet Francesco Andreoli
Michael J. Gullans
Alexander A. High
Antoine Browaeys
Darrick E. Chang
author_sort Francesco Andreoli
title Maximum Refractive Index of an Atomic Medium
title_short Maximum Refractive Index of an Atomic Medium
title_full Maximum Refractive Index of an Atomic Medium
title_fullStr Maximum Refractive Index of an Atomic Medium
title_full_unstemmed Maximum Refractive Index of an Atomic Medium
title_sort maximum refractive index of an atomic medium
publisher American Physical Society
publishDate 2021
url https://doaj.org/article/8d2183f95ec443508cf08c3d890fbadd
work_keys_str_mv AT francescoandreoli maximumrefractiveindexofanatomicmedium
AT michaeljgullans maximumrefractiveindexofanatomicmedium
AT alexanderahigh maximumrefractiveindexofanatomicmedium
AT antoinebrowaeys maximumrefractiveindexofanatomicmedium
AT darrickechang maximumrefractiveindexofanatomicmedium
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