How many particles do make a fluid? Qualifying collective behavior in expanding ultracold gases

Abstract

Collective phenomena in quantum many-body systems are often described in terms of hydrodynamics, an appropriate framework when the involved particle numbers are effectively macroscopic. We propose to use experiments on expanding clouds of few and many interacting cold atoms to investigate the emergence of hydrodynamics as a function of particle number. We consider gases confined in two-dimensional elliptically-deformed traps, and we employ the manifestation of elliptic flow as an indicator of collective behavior. We quantify the response of the gas to the deformation of the trapping potential, and show how such information can be used to establish how many atoms are needed for the system to develop a degree of collectivity comparable to that expected in the hydrodynamic limit. This method permits one, in particular, to exploit observations made in expanding atomic gases to shed light on the apparent hydrodynamic behaviour of mesoscopic systems of quarks and gluons formed in the scattering of light ions in high-energy collider experiments.

28 pages, 8 figures

References in corpus (13)

• Many-Body Physics with Ultracold Gases
• Theory of ultracold Fermi gases
• Triangularity and Dipole Asymmetry in Heavy Ion Collisions
• Triangular flow in hydrodynamics and transport theory
• Relativistic hydrodynamics for heavy-ion collisions
• Observation of deviations from ideal gas thermodynamics in a trapped Bose-Einstein condensed gas
• The smallest fluid on earth
• Shear viscosity of a universal Fermi gas near the superfluid phase transition
• Fluid Dynamics and Viscosity in Strongly Correlated Fluids
• Anisotropic expansion of a thermal dipolar Bose gas
• Development of transverse flow at small and large opacities in conformal kinetic theory
• A matter of shape: seeing the deformation of atomic nuclei at high-energy colliders
• Collective flow in single-hit QCD kinetic theory