Hanns-Christoph Nägerl, Institute for Experimental Physics, University of Innsbruck

"The wonder-full world of one-dimensional bosons"

Abstract: Laser-cooled bosons at ultralow temperatures, with strong interactions and under strong confinement, have myriad surprises in store. They don’t condense, instead fermionize, but remain superfluid, though at the slightest of perturbations they may crystallize. In our recent experiments with strongly confined Cs atoms, for which we can tune the contact interactions from zero to infinite, we have explored the 2D-to-1D crossover regime [1], implemented a very precise thermometer with which we have found cooling upon dimensional reduction [2], investigated into impurity transport through a fermionized Bose gas, analyzed the short-time dynamics in a quantum Newton cradle experiment, and found evidence for many-body dynamical localization in a 1D quantum kicked-rotor setting. In particular, we have seen that uniformly moving impurities develop anyonic properties, with anyons being quasi particles that interpolate between bosons and fermions. On the side, after 20 years of Bose-Einstein condensation of Cs atoms, we have condensed Cs atoms in a state other than the absolute ground state [3], and even that experiment has some surprise for us in store.

[1] Experimental observation of the 2D-1D dimensional crossover in strongly interacting ultracold bosons, Y. Guo et al., arXiv:2308.00411 (2023)

[2] Cooling bosons by dimensional reduction, Y. Guo et al., arXiv:2308.04144 (2023)

[3] Bose-Einstein condensation of non-ground-state caesium atoms, M. Horvath et al., arXiv:2310.12025 (2023)