Experimental observation of a generalized Gibbs ensemble

TLDR

In statistical mechanics, temperature indicates how far a system is from its lowest energy state, but in nonequilibrium quantum systems with multiple conserved quantities, this concept becomes more complex. The experiment demonstrated that up to ten temperature‑like parameters are required to characterize the steady state of a split one‑dimensional Rb gas. Langen et al., *Science*, issue p.207 (see also p.185).

Abstract

Detecting multiple temperatures Most people have an intuitive understanding of temperature. In the context of statistical mechanics, the higher the temperature, the more a system is removed from its lowest energy state. Things become more complicated in a nonequilibrium system governed by quantum mechanics and constrained by several conserved quantities. Langen et al. showed that as many as 10 temperature-like parameters are necessary to describe the steady state of a one-dimensional gas of Rb atoms that was split into two in a particular way (see the Perspective by Spielman). Science , this issue p. 207 ; see also p. 185