We consider quantum quench from a gapped to a gapless system in 1+1 dimensions. We
provide a rigorous proof of the thermalization of the reduced density matrix, hence that of
an arbitrary string of local operators in an interval. In case the system is integrable, the "thermalization" leads to a generalized Gibbs ensemble (GGE). We model the critical quench in terms of an initial state in terms of a conformal boundary state deformed by exponential cutoffs involving hamiltonian and other charges. We justify this choice of the initial state by explicitly
deriving it in free boson and free fermion systems with time-dependent mass. A surprising result we find is that for generic quenches and observables the higher charges remain
important even if the initial gap is arbitrarily high, contrary to standard RG expectations.
( based on hep-th/1501.04580 and a couple of upcoming papers)
- Quantum Fields and Strings
- Scientific Series