We have several experimental setups where we study of the effects of strong dipole-dipole interactions in systems of a few atoms:

• In the Rydberg project (CHADOQ), we use arrays of optical tweezers, each containing a single Rb atom, and we induce strong interactions between the atoms by exciting them to Rydberg states. We have basically full control over the system: geometry and size of the array, exact number of atoms, strength of the interaction… With this platform, we are currently exploring the physics of spin Hamiltonians with up to 200 particles.

• In the Nanocloud project (CYCLOPIX), we trap an adjustable number of Rb atoms (from 1 to 1000s) in microscopic dipole traps, either in ordered arrays or disordered very dense ensembles. We place ourselves in a regime where optical response of the cloud features collective effects, due to the strong interaction between light-induced dipoles.

• The Dysprosium project is under construction. We plan on assembling arrays of Dy atoms. Using the combination of narrow and broad lines of Dy, we plan on studying ordered ensembles of two-level atoms interacting via light-mediated interactions.
• In the ARCTIQ project, we explored how to combine trapping of single atoms in arrays of optical tweezers and a cryogenic environment at 4 K. The goal was to enhance dramatically the trapping lifetime of the atoms, in order to be able to arrange very large arrays of single atoms. We have demonstrated lifetimes of 6000 s for single atoms in optical tweezers, and the assembly of large defect-free arrays of 324 atoms. This experiment is now operated by PASQAL, in Massy, still in close collaboration with us.

• In our (now retired) vapor cell project, we studied the optical response of a hot (100°C – 200°C) vapor of alkali confined in a cell with thickness ranging from almost zero to one micrometer, i.e. comparable to the wavelength of an optical transition in Rb, Cs or K.