Characterising transport in a quantum gas by measuring Drude weights

TL;DR

This study measures Drude weights in a one-dimensional ultracold bosonic gas, validating hydrodynamic theories and demonstrating nearly dissipationless transport in strongly correlated quantum systems.

Contribution

It provides the first experimental measurement of Drude weights in an interacting quantum gas, confirming hydrodynamic predictions of ballistic transport at finite temperature.

Findings

Drude weights nearly fully characterize large-scale transport.

Transport is almost dissipationless even at finite temperatures.

Experimental results align with hydrodynamic theory predictions.

Abstract

Transport properties play a crucial role in defining materials as insulators, metals, or superconductors. A fundamental parameter in this regard is the Drude weight, which quantify the ballistic transport of charge carriers. In this work, we measure the Drude weights of an ultracold gas of interacting bosonic atoms confined to one dimension, characterising the induced atomic and energy currents in response to perturbations with an external potential. We induce currents through two distinct experimental protocols; by applying a constant force to the gas, and by joining two subsystems prepared in different equilibrium states. By virtue of integrability, dynamics of the system is governed by ballistically propagating, long-lived quasi-particle excitations, whereby Drude weights almost fully characterise large-scale transport. Indeed, our results align with predictions from a recently developed hydrodynamic theory, demonstrating almost fully dissipationless transport, even at finite temperatures and interactions. These findings not only provide experimental validation of the hydrodynamic predictions but also offer methodologies applicable to various condensed matter systems, facilitating further studies on the transport properties of strongly correlated quantum matter.