# Synopsis: Vindication for New Bose Gas Theory

Experiments confirm predictions of a new hydrodynamic approach to describing a 1D Bose gas, paving the way to better theories for more complex quantum gases.

One-dimensional systems of interacting particles offer researchers a window into macroscale quantum effects. To simplify analysis of such systems, researchers often treat them as continuous fluids rather than discrete bodies. However, this approach fails if the particles are not in thermal equilibrium. In 2016, researchers proposed a new hydrodynamic framework to solve this conundrum (see 27 December 2006 Viewpoint). Now, experiments show that this theory successfully describes the behavior of a 1D Bose gas as it is released from confinement, promising insights into a whole class of out-of-equilibrium many-body systems.

To test the theory, Max Schemmer, from the University of Paris-Sud, and colleagues confined clouds of several thousand rubidium atoms in a magnetic trap built from conducting wires a few millimeters long. They partially relaxed the confinement, allowing the cloud to spread along a single axis. The motion of the atoms in the first fraction of a second allowed the researchers to determine whether the new or the old theoretical framework agreed with observations. Both frameworks predict similar dynamics when the atoms start with a distribution having a single maximum density point, but only the new framework correctly predicts the gas’s evolution from a distribution having two peak density locations.

Theory and experiment did not conform perfectly, however. The atoms’ distribution deviated slightly from theory as the experiment progressed. The team attributes this to atoms gradually leaking from the cloud. Investigating this effect will be the next step, but the team also hopes to test the theory against other 1D atomic gases, such as strongly repulsive bosonic atoms and fermionic gases.

This research is published in Physical Review Letters.

–Marric Stephens

Marric Stephens is a freelance science writer based in Bristol, UK.

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## Subject Areas

Atomic and Molecular Physics

Quantum Physics

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