Non-Bloch $\mathcal{PT}$ symmetry breaking in non-Hermitian Photonic Quantum Walks

TL;DR

This paper explores how non-Hermitian photonic quantum walks exhibit non-Bloch $ ext{PT}$ symmetry breaking, revealing boundary-driven phase transitions and challenging traditional bulk-boundary correspondence in topological systems.

Contribution

It uncovers non-Bloch $ ext{PT}$ symmetry breaking in non-Hermitian quantum walks and proposes a method to detect boundary-driven phase transitions.

Findings

Non-Bloch $ ext{PT}$ symmetry breaking occurs in photonic quantum walks.

Boundary conditions significantly influence bulk properties in these systems.

A bulk probing method for boundary-driven phase transitions is proposed.

Abstract

A hallmark of topological band theory in periodic media is that bulk properties are not affected by boundary conditions. Remarkably, in certain non-Hermitian lattices the bulk properties are largely affected by boundaries, leading to such major effects as the non-Hermitian skin effect and violation of the bulk-boundary correspondence. Here we unveil that non-unitary discrete-time quantum walks of photons in systems involving gain and loss show rather generally non-Bloch parity-time ($\mathcal{PT}$) symmetry breaking phase transitions, and suggest a bulk probing method to detect such boundary-driven phase transitions.