Slow heterogeneous relaxation due to constraints in dual XXZ models

With the aim to understand the role of the constraints in the thermalization of quantum systems, we study the dynamics of a family of kinetically constrained models arising through duality from the XXZ spin chain. We find that integrable and nonintegrable deformations around the stochastic point give rise to ground state phase transitions between localised and delocalised phases, which in turn determine the nature of the relaxation dynamics at finite energy densities. While in the delocalised phase thermalization is fast and homogeneous, in the localised phase relaxation is slow, temporal autocorrelations exhibit plateaus indicative of metastability, and the growth of entanglement is heterogeneous in space. Furthermore, by considering relaxation from initial product states, we demostrate that this slow thermalization can be rationalised directly from the presence of constraints in the dynamics.