Frustration-induced emergent Hilbert space fragmentation

TL;DR

This paper investigates how frustration in quantum systems, especially on kagome lattices, causes Hilbert space fragmentation, leading to non-thermalizing behavior and complex relaxation dynamics, challenging traditional thermalization theories.

Contribution

It demonstrates Hilbert space fragmentation due to frustration in kagome lattice models, providing insights into non-thermalizing quantum dynamics beyond eigenstate thermalization.

Findings

Hilbert space fragmentation observed in kagome lattice models.

Fragmentation leads to a broad range of relaxation times.

Level statistics indicate deviations from thermal behavior.

Abstract

Although most quantum systems thermalize locally on short time scales independent of initial conditions, recent developments have shown this is not always the case. Lattice geometry and quantum mechanics can conspire to produce constrained quantum dynamics and associated glassy behavior, a phenomenon that falls outside the rubric of the eigenstate thermalization hypothesis. Constraints "fragment" the many-body Hilbert space due to which some states remain insulated from others and the system fails to attain thermal equilibrium. Such fragmentation is a hallmark of geometrically frustrated magnets with low-energy "icelike manifolds" exhibiting a broad range of relaxation times for different initial states. Focusing on the highly frustrated kagome lattice, we demonstrate these phenomena in the Balents-Fisher-Girvin Hamiltonian (easy-axis regime), and a three-coloring model (easy-plane regime), both with constrained Hilbert spaces. We study their level statistics and relaxation dynamics to develop a coherent picture of fragmentation in various limits of the XXZ model on the kagome lattice.