Generalized Hydrodynamics on an Atom Chip.

Area of Science:

• Quantum physics
• Condensed matter physics
• Atomic physics

Background:

• Emergent fluidlike behavior was theoretically predicted in one-dimensional (1D) quantum integrable systems out of equilibrium.
• Existing hydrodynamic approaches based on local thermal equilibrium failed to explain these phenomena.

Purpose of the Study:

• To experimentally establish the emergence of fluidlike behavior in 1D quantum integrable systems.
• To validate a dynamical extension of Yang-Yang thermodynamics for out-of-equilibrium systems.
• To compare experimental results with both novel and conventional hydrodynamic theories.

Main Methods:

• Monitoring the in situ density profile of a single 1D cloud of Rubidium-87 atoms trapped on an atom chip.
• Inducing a quench in the longitudinal trapping potential to initiate time evolution.
• Performing measurements on weakly interacting atomic clouds near the quasicondensate and ideal Bose gas crossover.

Main Results:

• Experimental observation of emergent fluidlike behavior at large scales, confirming theoretical predictions.
• Excellent agreement between experimental data and the novel hydrodynamic theory across various interaction strengths and temperatures.
• Demonstrated failure of the conventional hydrodynamic approach, which assumes local thermal equilibrium, to reproduce the observed dynamics.

Conclusions:

• The study provides the first experimental evidence for emergent hydrodynamics in 1D quantum integrable systems.
• The results validate a new theoretical framework that extends equilibrium thermodynamics to describe non-equilibrium quantum systems.
• This work highlights the limitations of traditional hydrodynamic models and opens new avenues for studying quantum dynamics out of equilibrium.