Effective two-level approximation of a multi-level system driven by coherent and incoherent fields

The numerical simulation of multiple scattering in dense ensembles is the mostly adopted solution to predict their complex optical response. While the scalar and vectorial light mediated interactions are accurately taken into account, the computational complexity still limits current simulations to the low saturation regime and ignores the internal structure of atoms. Here, we propose to go beyond these restrictions, at constant computational cost, by describing a multi-level system (MLS) by an effective two-level system (TLS) that best reproduces the coherent and total scattering properties in any saturation regime. The correspondence of our model is evaluated for different experimentally realistic conditions such as the modification of the driving field polarization, the presence of stray magnetic fields or an incoherent resonant electromagnetic field background. The trust interval of the model is quantified for the D2-line of 87Rb atoms but it could be generalized to any closed transition of a multi-level quantum system.Comment: 11 pages, 6 figure

Caracterization of the noise induce heating of cold atoms trapped in the near field of a nanostructured surface.

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Coupled dipole approach to sub-wavelength imaging in a dense atomic media

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Transport and coupling of a ultra-cold atomic gas with a nano-structured surface

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Absorption spectroscopy and atom number measurement of subwavelength volumes of cold atoms

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Molecular gas spectroscopy in hollow core fibers for atomic cooling using Telecom laser systems

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Quantitative absorption imaging of optically dense effective two-level systems

Absorption imaging is a commonly adopted method to acquire, with high temporal resolution, spatial information on a partially transparent object. It relies on the interference between a probe beam and the coherent response of the object. In the low saturation regime, it is well described by a Beer Lambert attenuation. In this paper we theoretically derive the absorption of a $\sigma$ polarized laser probe by an ensemble of two-level systems in any saturation regime. We experimentally demonstrate that the absorption cross section in dense $^{87}$Rb cold atom ensembles is reduced, with respect to the single particle response, by a factor proportional to the optical density b of the medium. To explain this reduction, we developed a model that incorporates, in the single particle response, the incoherent electromagnetic background emitted by the surrounding ensemble. We show that it qualitatively reproduces the experimental results. Our calibration factor that has a universal dependence on optical density $b$ for $\sigma$ polarized light : $\alpha$ = 1.17(9) + 0.255(2)b allows to obtain quantitative and absolute, in situ, images of dense quantum systems.Atomes Ultra-Froids piégés dans des Réseaux Optiques Nano-StructurésInitiative d'excellence de l'Université de Bordeau

Transport and coupling of a ultra-cold atomic gas with a nano-structured surface

International audienc

Doubly dressed state trapping

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Molecular gas spectroscopy in hollow core fibers for atomic cooling using Telecom laser systems

International audienc