Peculiar light-induced forces on atoms

In this talk I will present two “attractive” light-induced effects on atoms.

Recently, we investigated light induced dipole-dipole (LI-DD) interactions that are provoked by a spatially homogenous laser beam in a cloud of freely expanding atoms  [1]. This light-triggered collective effect results in a self-confining potential with interesting features: it exhibits nonlocal properties, it is attractive for both red and blue-detuned light fields, and it induces a strong force that depends on the gradient of the atomic density. For our experimental parameters we reach remarkably deep self-confining potentials corresponding to a trap depth of up to 8 µK. This LI-DD potential minimum is intrinsically tied to the atomic ensemble and can freely evolve in additional external potentials.

Using atom interferometric tools, we were able to investigate an attractive force on atoms caused by blackbody radiation [2].  Blackbody (thermal) radiation is emitted by objects at finite temperature with an outward energy-momentum flow, which exerts an outward radiation pressure. At room temperature e. g. a cesium atom scatters on average less than one of these blackbody radiation photons every 10⁸ years.  Thus, it is generally assumed that any scattering force exerted on atoms by such radiation is negligible. However, particles also interact coherently with the thermal electromagnetic field [3]and this leads to a surprisingly strong force acting in the opposite direction of the radiation pressure [2].

[1]         M. Maiwöger, M. Sonnleitner, T. Zhang, I. Mazets, M. Mallweger, D. Rätzel, F. Borselli, S. Erne, J. Schmiedmayer, and P. Haslinger, Observation of Light-Induced Dipole-Dipole Forces in Ultracold Atomic Gases, arXiv:2202.00562 (2022).

[2]         P. Haslinger, M. Jaffe, V. Xu, O. Schwartz, M. Sonnleitner, M. Ritsch-Marte, H. Ritsch, and H. Müller, Attractive Force on Atoms Due to Blackbody Radiation, Nat. Phys. 14, 257 (2018).

[3]         M. Sonnleitner, M. Ritsch-Marte, and H. Ritsch, Attractive Optical Forces from Blackbody Radiation, Phys. Rev. Lett. 111, 023601 (2013).