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Nuclear Physics Seminars at BNL

Observation of emergent hydrodynamic behavior in a mesoscopic 2D Fermi gas

by Giuliano Giacalone (ITP - Universität Heidelberg)


Emergent hydrodynamic behavior is observed in many-body systems across vastly different temperature scales. Motivated by the recent observation of collective particle emission in high-energy proton-proton collisions, where particle numbers are small and a fluid description is a priori inapplicable, we perform an experimental investigation of hydrodynamic behavior in two-dimensional Fermi gases with tunable particle number. To assess the emergence  of a collective expansion, we study the inversion of the shape of gases  prepared in elliptical traps. Shape inversion is a salient signature of an effective  pressure-gradient force, ascribable to hydrodynamics. To overcome the finiteness of the number of particles, experiments are repeated a statistically significant number of times, and statistical measures of the cloud shapes are devised. This is, hence, analogous to the analysis of collective behavior in the case of high-energy proton-proton experiments.

Clouds of few fermions, from 6 atoms up to 14 atoms, are found to exhibit strong collectivity. We conclusively determine that such observations emerge from atom-atom interactions occurring during the expansion of the system,
and can not be ascribed to underlying effects of quantum statistics. Interpreting these results as an emergent pressure-gradient force, we show that ideal hydrodynamic predictions closely match the experimental observations. We discuss the broad implications of this finding.

Organized by

Jiangyong Jia