Microscopic theory of the collective optical response of dilute atomic clouds at finite temperature

Abstract

At low temperature, collective light-induced dipole-dipole interactions are known to strongly reshape the optical response of atomic clouds, revealing the breakdown of the independent-scattering picture as the density increases. While thermal motion is generally believed to progressively suppress these interactions, the microscopic mechanisms behind this suppression remain largely unexplored. Here, we develop a microscopic theory of the optical response of a dilute atomic gas at finite temperature, explicitly accounting for atomic ballistic motion during the recurrent-scattering events associated with the collective corrections. Using a diagrammatic approach for scalar light, we derive the collective contribution to the optical permittivity and characterize its behavior across the full temperature range. We find that thermal corrections scale as ∼ T at low temperature, while recurrent-scattering contributions are suppressed as ∼ T^−3/2 at high temperature. Our predictions are confirmed by extensive coupled-dipole simulations that explicitly account for atomic motion. These simulations also reveal the inaccuracy of the modified frozen-dipole approximation commonly used to treat thermal effects. Finally, extending our theory to vector light, we provide a complete picture of how the resonance shift continuously evolves from the collective Lamb shift at low temperatures to the classical Lorentz-Lorenz shift at high temperatures.

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BibTeX RIS

BibTeX

@misc{schoger2026microscopic,
  title = {{Microscopic theory of the collective optical response of dilute atomic clouds at finite temperature}},
  author = {Tanja Schoger and Romain Pierrat and Nicolas Cherroret},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.29786},
  eprint = {2609.29786},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.29786},
}

RIS

TY  - UNPB
TI  - Microscopic theory of the collective optical response of dilute atomic clouds at finite temperature
AU  - Tanja Schoger
AU  - Romain Pierrat
AU  - Nicolas Cherroret
PY  - 2026
DA  - 2026/09/24
PB  - arXiv
DO  - 10.48550/arxiv.2609.29786
UR  - https://arxiv.org/abs/2609.29786
AB  - At low temperature, collective light-induced dipole-dipole interactions are known to strongly reshape the optical response of atomic clouds, revealing the breakdown of the independent-scattering picture as the density increases. While thermal motion is generally believed to progressively suppress these interactions, the microscopic mechanisms behind this suppression remain largely unexplored. Here, we develop a microscopic theory of the optical response of a dilute atomic gas at finite temperature, explicitly accounting for atomic ballistic motion during the recurrent-scattering events associated with the collective corrections. Using a diagrammatic approach for scalar light, we derive the collective contribution to the optical permittivity and characterize its behavior across the full temperature range. We find that thermal corrections scale as ∼ T at low temperature, while recurrent-scattering contributions are suppressed as ∼ T^−3/2 at high temperature. Our predictions are confirmed by extensive coupled-dipole simulations that explicitly account for atomic motion. These simulations also reveal the inaccuracy of the modified frozen-dipole approximation commonly used to treat thermal effects. Finally, extending our theory to vector light, we provide a complete picture of how the resonance shift continuously evolves from the collective Lamb shift at low temperatures to the classical Lorentz-Lorenz shift at high temperatures.
ER  -

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