Freezing transition in particle-conserving East model

TL;DR

This paper investigates a particle-conserving East model revealing a sharp transition from thermalizing to frozen dynamics as particle density varies, with exact critical exponents and universality class identified.

Contribution

It introduces a minimal particle-conserving East model exhibiting a filling-induced freezing transition with analytically derived critical behavior.

Findings

Sharp transition from weak to strong fragmentation at critical density

Exact critical exponents obtained for the phase transition

Transition belongs to the universality class of dipole-conserving fracton systems

Abstract

Quantum kinetically constrained models can exhibit a wealth of dynamical phenomena ranging from anomalous transport to Hilbert-space fragmentation (HSF). We study a class of one-dimensional particle number conserving systems where particle hoppings are subjected to an East-like constraint, akin to facilitated spin models in classical glasses. While such a kinetic constraint leads to HSF, we find that the degree of fragmentation exhibits a sharp transition as the average particle density is varied. Below a critical density, the system transitions from being weakly fragmented where most of the initial states thermalize diffusively, to strongly fragmented where the dynamics are frozen and the system fails to thermalize. Remarkably, the East model allows for both efficient numerical simulations and analytic solutions of various diagnostics of the phase transition, from which we obtain a set of exact critical exponents. We find that the freezing transition in particle-conserving East models belongs to the same universality class as dipole-conserving fracton systems. Our results provide a tractable minimal model for filling-induced freezing transitions associated with HSF, which can be readily tested in state-of-the-art quantum platforms.