Nonparaxiality-triggered Landau-Zener transition in topological photonic waveguides

TL;DR

This paper investigates how nonparaxial wave propagation in topological photonic waveguides influences energy spectrum transitions, revealing effects that differ from paraxial approximations and enabling new dynamic state transfer applications.

Contribution

It demonstrates the impact of nonparaxiality on Landau-Zener transitions and boundary state transfer in topological photonic lattices, expanding understanding beyond paraxial models.

Findings

Nonparaxiality causes stretched and compressed forces on the energy spectrum.

Expansion of a band gap supports adiabatic boundary state transfer.

Narrowing of a band gap induces Landau-Zener transition.

Abstract

Photonic lattices have been widely used for simulating quantum physics, owing to the similar evolutions of paraxial waves and quantum particles. However, nonparaxial wave propagations in photonic lattices break the paradigm of the quantum-optical analogy. Here, we reveal that nonparaxiality exerts stretched and compressed forces on the energy spectrum in the celebrated Aubry-Andre-Harper model. By exploring the mini-gaps induced by the finite size of the different effects of nonparaxiality, we experimentally present that the expansion of one band gap supports the adiabatic transfer of boundary states while Landau-Zener transition occurs at the narrowing of the other gap, whereas identical transport behaviors are expected for the two gaps under paraxial approximation. Our results not only serve as a foundation of future studies of dynamic state transfer but also inspire applications leveraging nonparaxial transitions as a new degree of freedom.