Light-matter interaction is well understood on the single-atom level and routinely used to manipulate atomic gases. However, in denser ensembles, collective effects emerge that are caused by light-induced dipole-dipole interactions and multiple photon scattering. Here, we report on the observation of a mechanical deformation of a cloud of ultracold ${}^{87}\mathrm{Rb}$ atoms due to the collective interplay of the atoms and a homogenous light field. This collective light scattering results in a self-confining potential with interesting features: It exhibits nonlocal properties, is attractive for both red- and blue-detuned light fields, and induces a remarkably strong force that depends on the gradient of the atomic density. Our experimental observations are discussed in the framework of a theoretical model based on a local-field approach for the light scattered by the atomic cloud. Our study provides a new angle on light propagation in high-density ensembles and expands the range of tools available for tailoring interactions in ultracold atomic gases.

中文翻译：

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超冷原子气体中光致偶极-偶极力的观察

光与物质的相互作用在单原子水平上得到了很好的理解，并经常用于操纵原子气体。然而，在更密集的系综中，出现了由光诱导的偶极-偶极相互作用和多光子散射引起的集体效应。在这里，我们报告了对超冷云的机械变形的观察${}^{87}铷$由于原子的集体相互作用和均匀的光场。这种集体光散射产生了具有有趣特征的自限制潜力：它表现出非局部特性，对红色和蓝色失谐光场都具有吸引力，并产生取决于原子密度梯度的非常强的力。我们的实验观察是在一个理论模型的框架内讨论的，该模型基于原子云散射的光的局部场方法。我们的研究为高密度系综中的光传播提供了一个新角度，并扩大了可用于定制超冷原子气体中相互作用的工具范围。