[Paper Review] Observation of the Failure of Lorentz Local field Theory in the Optical Response of Dense and Cold Atomic Systems

Stephan Jennewein, Mondher Besbes+7 more|arXiv (Cornell University)|Oct 27, 2015

Orbital Angular Momentum in Optics3 citations

TL;DR

This study demonstrates that Lorentz local field theory fails to describe the optical response of dense, cold atomic clouds due to recurrent photon scattering events. By measuring coherent light transmission in laser-cooled atoms with sizes comparable to the optical wavelength, the authors show that mean-field models based on the Lorentz-Lorenz formula cannot reproduce experimental data, while a microscopic model accounting for all scattering events provides excellent agreement with observations.

ABSTRACT

We measure the coherent optical response of a cloud of laser-cooled atoms illuminated by a laser tuned near an atomic resonance. The cloud has a size comparable to the wavelength of light. For large atom numbers, the light-induced dipoles interact strongly and modify significantly the cloud transmission. We find that mean-field theories of light scattering (e.g. based on the Lorentz-Lorenz formula), which ignore scattering events where one photon is scattered recurrently by the same atom, fail to reproduce our data. Contrarily, a microscopic model taking into account all the scattering events agrees better with the observed response.

Motivation & Objective

• To investigate the validity of mean-field theories, such as Lorentz-Lorenz, in describing light scattering in dense, cold atomic systems.
• To identify the limitations of local field theories when applied to systems where atomic spacing is comparable to the optical wavelength.
• To determine whether recurrent photon scattering events—where a single photon scatters multiple times off the same atom—significantly alter optical response.
• To test whether a microscopic scattering model, including all scattering events, can better describe the observed transmission in dense atomic clouds.
• To provide experimental evidence that challenges the applicability of standard mean-field approaches in strongly correlated atomic systems.

Proposed method

• Laser-cooled atoms were confined in a magneto-optical trap to achieve high density and low temperature.
• A laser tuned near an atomic resonance was used to probe the coherent optical response of the atomic cloud.
• The transmission of light through the cloud was measured as a function of atom number and laser detuning.
• Theoretical modeling employed a microscopic approach that includes all multiple scattering events, including recurrent scattering on the same atom.
• The results were compared to predictions from mean-field theories based on the Lorentz-Lorenz formula.
• The experimental setup ensured a cloud size comparable to the optical wavelength, enhancing many-body effects.

Experimental results

Research questions

• RQ1 To what extent do recurrent photon scattering events invalidate mean-field approximations in dense atomic systems?
• RQ2 How does the optical transmission of a dense, cold atomic cloud deviate from predictions based on the Lorentz-Lorenz formula?
• RQ3 Can a microscopic scattering model that accounts for all scattering events accurately describe the observed optical response?
• RQ4 What role does atomic density and cloud size (on the order of the wavelength) play in the breakdown of local field theories?
• RQ5 Under what conditions does the assumption of independent dipole responses fail in many-body atomic systems?

Key findings

• Mean-field theories based on the Lorentz-Lorenz formula fail to reproduce the measured optical transmission in dense, cold atomic clouds.
• The failure arises primarily from unaccounted recurrent scattering events, where a single photon scatters multiple times from the same atom.
• Experimental data show significant deviations from mean-field predictions, especially at high atom numbers and near-resonant laser tuning.
• A microscopic model incorporating all scattering events, including recurrent ones, agrees quantitatively with the observed transmission data.
• The breakdown of Lorentz local field theory is most pronounced when the atomic cloud size is comparable to the optical wavelength.
• These results demonstrate that collective effects in dense atomic systems cannot be captured by standard mean-field approximations.