Two-dimensional Thouless pumping of light in photonic moir\'e lattices

TL;DR

This paper demonstrates the first experimental realization of two-dimensional topological Thouless pumping of light in photonic moiré lattices, revealing quantized transport phenomena driven by topological properties.

Contribution

It introduces a novel photonic system for observing 2D Thouless pumping using photorefractive moiré lattices, combining experimental observation with numerical simulations.

Findings

Observation of quantized beam shift over a pumping cycle

Confirmation of topological nature through shift magnitude and direction

Platform for exploring topological effects in tunable geometries

Abstract

Continuous and quantized transports are profoundly different. The latter is determined by the global rather than local properties of a system, it exhibits unique topological features, and its ubiquitous nature causes its occurrence in many areas of science. Here we report the first observation of fully-two-dimensional Thouless pumping of light by bulk modes in a purpose-designed tilted moir\'e lattices imprinted in a photorefractive crystal. Pumping in such unconfined system occurs due to the longitudinal adiabatic and periodic modulation of the refractive index. The topological nature of this phenomenon manifests itself in the magnitude and direction of shift of the beam center-of-mass averaged over one pumping cycle. \rev{Our experimental results are supported by systematic numerical simulations in the frames of the continuous Schr\"{o}dinger equation governing propagation of probe light beam in optically-induced photorefractive moir\'e lattice.} Our system affords a powerful platform for the exploration of topological pumping in tunable commensurate and incommensurate geometries.