Abstract：

Laser-cooled bosons at ultralow temperatures, with strong interactions and under strong low-dimensional 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 [3]. 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 [4], and even that experiment has some surprise for us in store.

[1] Observation of the 2D-1D dimensional crossover in strongly interacting ultracold bosons,

Y. Guo et al., Nature Physics (2024), arXiv:2308.00411 (2023)

[2] Anomalous cooling of bosons by dimensional reduction,

Y. Guo et al., Science Advances 10, 6 (2024), arXiv:2308.04144 (2023)

[3] Observation of many-body dynamical localization,

Y. Guo et al., arXiv:2312.13880 (2023)

[4] Bose-Einstein condensation of non-ground-state caesium atoms,

M. Horvath et al., Nature Communications 15, 3739 (2024), arXiv:2310.12025 (2023)

Speaker's Brief Introduction：

Hanns-Christoph Nägerl studied physics in Göttingen, San Diego, and Innsbruck and completed his doctoral thesis in 1998 on the subject of “Ion Strings for Quantum Computation” with Prof. R. Blatt. As a postdoctoral researcher he work at the California Institute of Technology (Caltech) with Prof. J. Kimble on single ultracold neutral atoms for quantum information purposes. In 2000 he joined Prof. R. Grimm in Innsbruck to set up an ultracold-atom group and to work on atomic and molecular quantum gases and matter waves. He received his “habilitation” in 2006, with this became associate professor, and then advanced to full professor for experimental physics at the University of Innsbruck in 2011. Professor Nägerl has been awarded numerous prizes, e.g. a START prize grant (2003), the Rudolf-Kaiser prize (2010), an ERC-Consolidator prize grant (2011), the prestigious Wittgenstein award (2017), and an ERC-Advanced prize grant (2018). Presently, he is the director of the Institute for Experimental Physics of the University of Innsbruck. His scientific interests center on quantum many-body physics and quantum simulation on the basis of ultracold atoms and molecules.