Locality versus Fock-space structure in East-type models

TL;DR

This paper investigates how the structure of Fock space connectivity influences phase transitions in East-type quantum models, showing that Fock space organization, not real-space locality, governs localization phenomena.

Contribution

It demonstrates that the Fock space graph structure, rather than geometric locality, is crucial for phase transitions in East-type constrained quantum models.

Findings

A transition exists between delocalised and localised phases despite nonlocal Fock space connectivity.

Fock space organization determines localization, independent of real-space locality.

Randomising Fock space connectivity preserves the phase transition in East-type models.

Abstract

Local kinetic constraints in quantum many-body systems can generate slow dynamics or complete many-body localisation. Here we focus on a modification of the quantum East model: Inspired by random matrix theory, we randomise the connectivity in Fock space (rendering it nonlocal in real space) while preserving its organisation into neighbouring magnetisation sectors. We find that there is still a transition between two distinct phases, one delocalised and the other localised. We conclude that, for East-type constrained models, the essential ingredient is the structure of the graph in Fock space rather than geometric locality of spin flips.