It is widely accepted that local subsystems in isolated integrable quantum systems equilibrate to generalized Gibbs ensembles. Here, we demonstrate the failure of canonical generalized thermalization for a particular class of initial states in certain types of interacting integrable models. Particularly, we show that in the easy-axis regime of the quantum XXZ chain, pure non-equilibrium initial states with no magnetic fluctuations instead locally relax to squeezed generalized Gibbs ensembles, referring to exotic equilibrium states governed by non-local equilibrium Hamiltonians with sub-extensive charge fluctuations that violate the self-affine scaling. The behaviour at the isotropic point is exceptional and depends on the initial state. We find that relaxation from the Néel state is governed by extensive fluctuations and a super-diffusive dynamical exponent compatible with the Kardar-Parisi-Zhang universality. On the other hand, there are other non-fluctuating initial states that display diffusive scaling. Our predictions can be directly tested in state-of-the-art cold atomic experimental settings.
- Pub Date:
- March 2023
- Condensed Matter - Quantum Gases;
- Condensed Matter - Statistical Mechanics;
- Nonlinear Sciences - Exactly Solvable and Integrable Systems
- typos corrected, refs added