Simulating non-Hermitian quasicrystals with single-photon quantum walks

TL;DR

This paper experimentally simulates non-Hermitian quasicrystals using photonic quantum walks, revealing phase transitions related to non-Hermitian skin effects and PT-symmetry breaking, with results confirming topological predictions.

Contribution

It introduces an experimental approach to simulate non-Hermitian quasicrystals and demonstrates phase transitions linked to spectral topology in open quantum systems.

Findings

Observation of transition from delocalized to localized phases

Confirmation of spectral winding number as critical point indicator

Detection of non-Hermitian skin effects in photonic quantum walks

Abstract

Non-Hermiticity significantly enriches the properties of topological models, leading to exotic features such as the non-Hermitian skin effects and non-Bloch bulk-boundary correspondence that have no counterparts in Hermitian settings. Its impact is particularly illustrating in non-Hermitian quasicrystals where the interplay between non-Hermiticity and quasiperiodicity results in the concurrence of the delocalization-localization transition, the parity-time (PT)-symmetry breaking, and the onset of the non-Hermitian skin effects. Here we experimentally simulate non-Hermitian quasicrystals using photonic quantum walks. Using dynamic observables, we demonstrate that the system can transit from a delocalized, PT-symmetry broken phase that features non-Hermitian skin effects, to a localized, PT-symmetry unbroken phase with no non-Hermitian skin effects. The measured critical point is consistent with the theoretical prediction through a spectral winding number, confirming the topological origin of the phase transition. Our work opens the avenue of investigating the interplay of non-Hermiticity, quasiperiodicity, and spectral topology in open quantum systems.