Topological Pumping Through a Localized Bulk in a Photonic Hofstadter System

TL;DR

This paper demonstrates topological pumping in a photonic system using a multilayer photonic crystal, revealing a transition from adiabatic to Landau-Zener-mediated transport as quasiperiodic modulation increases.

Contribution

It introduces a photonic realization of the Hofstadter model with tunable quasiperiodicity, showing localization transitions and persistent edge states in a compact system.

Findings

Observation of Hofstadter butterfly and chiral edge states in photonics

Localization transition induced by quasiperiodic modulation

Transition from adiabatic to Landau-Zener topological pumping

Abstract

Photonic systems provide a highly tunable platform for emulating quantum Hall physics. This tunability enables probing of the interplay between strong disorder and robust topological transport that remains difficult to access in solid-state systems. Here we realize a photonic version of the Harper-Hofstadter and Aubry-Andr\'e models using a one-dimensional multilayer photonic crystal (Bragg stack) with a synthetic dimension encoded in its geometry. By modulating the layer thicknesses, we observe the Hofstadter butterfly and its chiral edge states from a family of one-dimensional multilayer structures, consistent with the Thouless pump picture. Exploiting the quasiperiodicity in this model, we show that increasing quasiperiodic modulation induces a wavelength-selective localization transition: specific Chern bands become fully localized along one dimension, while chiral edge states persist and continue to wind across the gap. We confirm this behavior through numerical simulations and experiments, and eigenmode analysis reveals that edge transport in this regime proceeds via a sequence of Landau-Zener transitions between localized states. These results demonstrate a crossover from adiabatic Thouless pumping under weak quasiperiodic modulation to a Landau-Zener-mediated topological pump at strong modulation, realized in a a compact and easily tunable photonic system.