ICTS

I will present an elementary, general, and semi-quantitative description of relaxation to gaussian and generalized Gibbs states in models of fermions or bosons with quadratic hamiltonians. The arguments apply to arbitrary initial states that satisfy a weak condition on clustering of correlations. I will also show that similar arguments can be used to understand relaxation (or its absence) in systems with time-dependent quadratic Hamiltonians, and provide a semi-quantitative description of relaxation in quadratic periodically driven (“Floquet”) systems.