Does quantum chaos explain quantum statistical mechanics?

If a many-body quantum system approaches thermal equilibrium from a generic initial state, then the expectation value 〈ψ(t)|Ai|ψ(t)〉, where |ψ(t)〉 is the system’s state vector and Ai is an experimentally accessible observable, should approach a constant value which is independent of the initial state, and equal to a thermal average of Ai at an appropriate temperature. We show that this is the case for all simple observables whenever the system is classically chaotic. Typeset using REVTEX ∗ E–mail: [email protected]