Characterizing transport in a quantum gas by measuring Drude weights

Transport properties define materials as insulators, metals, or superconductors. A fundamental parameter is the Drude weight, which quantifies the ballistic transport of charge carriers. Here, we measure the Drude weights of an ultracold gas of interacting bosonic atoms confined to one dimension, characterizing atomic and energy currents induced by applying a constant force and by joining two subsystems prepared in different equilibrium states. We demonstrate dissipationless transport, even in the presence of interactions and finite temperature, signifying ballistic propagation of conserved quantities corresponding to lowest order hydrodynamics. Our approach provides a robust and transparent framework for characterizing transport in strongly correlated quantum matter, applicable in regimes where theory remains incomplete.