Ground state and persistent oscillations in the quantum East model

TL;DR

This paper investigates the ground state and persistent oscillations in the 1D quantum East model, revealing boundary-driven phenomena and identifying simple states that capture complex quantum behaviors.

Contribution

It demonstrates that in the limit of large negative s, the ground state and certain excited states are well approximated by simple spin-coherent product states, highlighting boundary effects.

Findings

Ground state accurately captured by spin-coherent product state at s → -∞

Existence of a low-entanglement excited eigenstate with boundary spin rotation

Persistent oscillations due to boundary physics, not quantum scars

Abstract

For the 1D quantum East model with open boundaries, we show that in the limit $s \to -\infty$, the ground state is accurately captured by a simple spin-coherent product state. We further identify a low-entanglement excited eigenstate that differs from the ground state only by a $\pi$-rotation of the boundary spin, remaining well approximated by a spin-coherent state. For a range of $-\infty<s<0$, the edge-coherent product state overlaps with two eigenstates separated by a size-independent energy gap, leading to persistent coherent oscillations of both global and local observables in the thermodynamic limit. These oscillations originate from boundary physics and are distinct from quantum many-body scars or hypercube-like Fock-space mechanisms.