Møller, Frederik - Vienna University of Technology

Emergent hydrodynamics and Pauli blocking in quasi-1D Bose gases

Many-body quantum systems with reduced dimensionality often exhibit properties strikingly different from that of three-dimensional (3D) systems. Confinement of atoms to a single line (1D) leads, for example, to strongly correlated motion of the atoms. The resulting collective excitations are quasi-particles, whose properties may differ significantly from the atoms; in a Bose gas, correlation effects due to interactions in 1D prevent two collective excitations from occupying the same quantum state. This imposed Pauli exclusion leads to effective fermionization of the quantum Bose gas in 1D even for weak interatomic repulsion; similar fermionization in 3D occurs only for extremely strong repulsion.

In our experiment we show that these theoretical concepts have far-reaching consequences even in real systems which always are only approximately 1D. We prepare a Bose gas of weakly interacting rubidium atoms under tight transverse confinement on an AtomChip. Next, we perturb the system to initiate dynamics and monitor its relaxation by measuring the atomic density. Tuning the temperature allows us to probe the regime where a non-negligible fraction of atoms have sufficiently high energy to cause transverse excitations. Even in this regime, far beyond conventional limits of 1D, the system relaxes slowly in agreement with 1D physics of effective fermionization of the quantum Bose gas. Our observations represent a manifestation of the emergent Pauli blocking of excitations, whereby our system remains effectively 1D.