Triggering Boundary Phase Transitions through Bulk Measurements in 2D Cluster States

TL;DR

This paper explores how bulk measurements in a 2D cluster state induce different boundary phase transitions, revealing complex entanglement behaviors and phases that resemble cat states with spontaneous symmetry breaking.

Contribution

It uncovers the boundary phase diagram of a 2D cluster state under measurements, showing volume-law and area-law entanglement phases and identifying a noninjective matrix product state phase.

Findings

Boundary exhibits volume-law entanglement at $ heta = rac{\pi}{2}$.

Boundary exhibits area-law entanglement for $ heta < rac{\pi}{2}$.

A phase transition occurs at $ heta_c=1.371$ within the area-law phase.

Abstract

We investigate the phase diagram at the boundary of an infinite two-dimensional cluster state subject to bulk measurements using tensor network methods. The state is subjected to uniform measurements $M = \cos{\theta}Z+\sin{\theta}X$ on the lower boundary qubits and in all bulk qubits. Our results show that the boundary of the system exhibits volume-law entanglement at the measurement angle $\theta = \pi/2$ and area-law entanglement for any $\theta < \pi/2$. Within the area-law phase, a phase transition occurs at $\theta_c=1.371$. The phase with $\theta \in(\theta_c,\pi/2)$ is characterized by a noninjective matrix product state, which cannot be realized as the unique ground state of a one-dimensional local, gapped Hamiltonian. Instead, it resembles a cat state with spontaneous symmetry breaking. These findings demonstrate that the phase diagram of the boundary of a two-dimensional system can be more intricate than that of a standard one-dimensional system.