Quantum interferences and Boltzmann theory

Abstract

The transport properties of dilute spin-polarized gases are studied. We first review the modifications of the standard Boltzman equation due to various interference effects induced by quantum indistinguishability. We then focus on two properties that have been the object of experimental studies: heat conduction and oscillatory spin diffusion. The convergence of the moment expansion of the out of equilibrium density matrix is checked. As is well known, this convergence is rapid in the “standard cases” of heat conductivity and spin diffusion in unpolarized gases. However, it appears to be much slower when exchange processes are dominant as is the case for spin waves or for heat conduction in polarized gases. In these two situations the first approximation is very poor and can be 15% to 20% off the exact result. Four to five moments are then necessary to achieve a one percent accuracy. Variations of the results with the choice of various modern potentials are displayed for the helium case and comparisons with experiments are made.