Probing ultracold 1D systems out of equilibrium
Manuele Landini (University of Innsbruck)
I will present the activities of our group, going under the broad topic of out of equilibrium phenomena in ultracold 1D gases. In our experiment, an ensemble of a few thousand effectively one dimensional ultracold Cs samples, each containing 10 to 30 atoms is prepared and investigated. Careful control over the trapping potential, temperature and interaction energy enables the investigation of collective quantum transport behavior of these systems and the preparation of out of equilibrium states with unusual statistical properties. The control over interaction strength in our Cs experiment allows us to perform topological pumping experiments by cycling the value of the coupling constant. In each cycle, the system is promoted to increasingly more energetic many-body states, stabilized by approximate integrability. These states are characterized by the presence of fractional Fermi seas (FFS) resulting from effective “hyperfermionic” statistics, where each particle occupies more than one quantum state. The creation of the FFS is inferred in the experiment by the direct observation of Friedel oscillations in the g1 correlation function of the gas [1,2]. Introducing spin impurities with variable speed in the 1D gas, we were able to characterize their relaxation dynamics and infer the formation of a polaron, resulting in finite long-time velocity of the impurity, even though the system is not in a standard superfluid state [3]. By slowly accelerating the impurity across the polaronic dispersion, we could observe its momentum distribution, revealing a cross-over in the effective statistical behavior of the system from bosonic to fermionic, passing from the anyonic intermediate statistics as a function of the injected momentum [4].
[1] Realization of fractional Fermi seas, Y. Zeng, A. Bastianello, S. Dhar, Z. Wang, X. Yu, M. Horvath, G. E. Astrakharchik, Y. Guo, H.-C. Nägerl, M. Landini, arXiv:2602.17657 (2026).
[2] Exotic critical states as fractional Fermi seas in the one-dimensional Bose gas, A. Bastianello, Y. Zeng, S. Dhar, Z. Wang, X. Yu, M. Horvath, G. E. Astrakharchik, Y. Guo, H.-C. Nägerl, M. Landini, arXiv:2602.17656 (2026).
[3] Observing dissipationless flow of an impurity in a strongly repulsive quantum fluid, M. Horvath, S. Dhar, E. Wybo, D. Trypogeorgos, Y. Guo, M. B. Zvonarev, M. Knap, M. Landini, H.-C. Nägerl, arXiv:2602.12320 (2026).
[4] Observing anyonization of bosons in a quantum gas, S. Dhar, B. Wang, M. Horvath, A. Vashisht, Y. Zeng, M. B. Zvonarev, N. Goldman, Y. Guo, M. Landini, H.-C. Nägerl, Nature, 642, 53–57 (2025).