New states in one-dimensional ultracold bosons with varying interactions
Alvise Bastianello (Université Dauphine)
Quantum statistics governs ultracold matter: bosons can condense and are generally unstable when interactions are attractive. In contrast, fermions form Fermi seas and avoid collapse when attractive via the Pauli principle exclusions. In one dimension, interactions and statistics intertwine, blurring this distinction, and approximate integrability stabilizes novel phases.
In this talk, I present recent experimental and theoretical results on ultracold bosons driven out of equilibrium by time-dependent interactions. In the first experiment, we realized Fermi sea-like states with fractional occupancy, which we dub fractional Fermi seas (FFS). These FFS showcase prominent Friedel oscillations in the one-particle correlator detected in the experiment, and bear clear signatures of criticality beyond the Luttinger Liquid paradigm.
In the second experiment, we gently swipe interactions from the repulsive to the attractive regime, promoting the formation of a gas of stable bound states called Bethe strings, whose binding energy leaves a clear signature in the experimentally observed momentum distribution.
Experimental data are in quantitative agreement with theoretical predictions from Generalized Hydrodynamics, which provide a comprehensive characterization of these exotic nonequilibrium states.