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 87Rb 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.

M. Maiwöger, M. Sonnleitner, T. Zhang, I. Mazets, M. Mallweger, D. Rätzel, F. Borselli, S. Erne, J. Schmiedmayer, P. Haslinger, “Observation of Light-Induced Dipole-Dipole Forces in Ultracold Atomic Gases”, Phys. Rev. X 12, 031018 (2022).


Related to Project A03