26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Applicability of conventional hydrodynamics to finite-temperature 1D Bose gases

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral AIP | Quantum Science and Technology (QST)

Description

One-dimensional Bose gases with repulsive contact interactions provide a paradigmatic example of an integrable quantum many-body system. Realized experimentally with ultracold atoms and described theoretically by the exactly solvable Lieb–Liniger model, they have become an important platform for studying non-equilibrium quantum dynamics.

Despite the exact solvability of the Lieb–Liniger model, describing its nonequilibrium many-body dynamics remains a formidable challenge. A natural approximate framework for describing large-scale dynamics is hydrodynamics. However, the integrability of the Lieb–Liniger model implies the existence of infinitely many conserved charges, suggesting that the appropriate hydrodynamic description is the recently discovered theory of generalized hydrodynamics (GHD) rather than the well-known theory of conventional (Euler) hydrodynamics, which incorporates only particle-number, momentum, and energy conservation. It is therefore not obvious under which conditions, if any, conventional hydrodynamics, being considerably simpler than GHD, could remain quantitatively accurate.

Here, we address this question by systematically benchmarking conventional hydrodynamics against GHD. We quantify the differences between the two approaches and establish criteria under which GHD effectively reduces to the conventional description. We determine the regime of validity of conventional hydrodynamics across the full range of interaction strengths, from the weakly interacting Bogoliubov regime to the strongly interacting Tonks–Girardeau regime, and from the low-temperature quantum-degenerate regime to the high-temperature classical regime. Our results provide practical bounds on the applicability of conventional hydrodynamics, thereby identifying when this well-established framework remains quantitatively reliable and when a generalized-hydrodynamic description becomes necessary for characterising phenomena such as sound propagation, collective oscillations, and expansion dynamics.