2009/04/30 by Thomas Schäfer, Thomas Schaefer, Derek Teaney · 13 citations
Physics and Astronomy · #Boltzmann constant #Cold Atom Physics and Bose-Einstein Condensates #Electron #Fermi gas #High-Energy Particle Collisions Research #Physics #Plasma #Quantum electrodynamics #Quantum mechanics #Quantum, superfluid, helium dynamics #Quark #Quark–gluon plasma #String theory #cond-mat.quant-gas #hep-lat #hep-ph #hep-th #nucl-th
paper · pdf · doi:10.1088/0034-4885/72/12/126001
published as Rept.Prog.Phys.72:126001,2009 · 76 pages, 11 figures, review article, extensive revisions
arxiv created 2009/07/17 · openalex publication_date 2009/11/12 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
Shear viscosity is a measure of the amount of dissipation in a simple fluid. In kinetic theory shear viscosity is related to the rate of momentum transport by quasi-particles, and the uncertainty relation suggests that the ratio of shear viscosity η to entropy density s in units of ℏ/ k B is bounded by a constant. Here, ℏ is Planck's constant and k B is Boltzmann's constant. A specific bound has been proposed on the basis of string theory where, for a large class of theories, one can show that η/ s ⩾ ℏ/(4π k B ). We will refer to a fluid that saturates the string theory bound as a perfect fluid. In this review we summarize theoretical and experimental information on the properties of the three main classes of quantum fluids that are known to have values of η/ s that are smaller than ℏ/ k B . These fluids are strongly coupled Bose fluids, in particular liquid helium, strongly correlated ultracold Fermi gases and the quark gluon plasma. We discuss the main theoretical approaches to transport properties of these fluids: kinetic theory, numerical simulations based on linear response theory and holographic dualities. We also summarize the experimental situation, in particular with regard to the observation of hydrodynamic behavior in ultracold Fermi gases and the quark gluon plasma.