Photonic state engineering via energy-level crossing by giant atoms in topological waveguide QED setup

TL;DR

This paper introduces a novel method for photonic state engineering using nonlocal giant-atom coupling in topological waveguide QED, enabling controlled state manipulation via energy-level crossings.

Contribution

It demonstrates a new mechanism combining topological band structure and giant-atom coupling for programmable photonic state control in waveguide QED.

Findings

Achieves high-fidelity conversion of spatially split states into combined states.

Realizes robust photon transfer through sequential in-gap crossings.

Shows controllable energy-level crossing protected by topological gap.

Abstract

Photonic state engineering in waveguide QED is typically based on local light-matter interactions. This limits its control over the spatial structure of bound photonic states. Here, we demonstrate a distinct mechanism arising from the interplay between nonlocal giant-atom coupling and topological band structure. Specifically, we consider giant atoms coupled to a Su-Schrieffer-Heeger waveguide and show that this configuration enables a controllable energy-level crossing protected by the topological gap. Adiabatically sweeping the atomic detuning across the crossing leads to a controlled exchange between distinct photonic bound states. In a two-giant-atom configuration, this mechanism achieves high-fidelity conversion of a spatially splitting state into a combining state. Extending this scheme to three-giant atoms, we further realize robust, shape-preserving photon transfer mediated by sequential in-gap crossings. Our results demonstrate how topology and nonlocal light-matter coupling can be combined to achieve programmable control of bound photonic states in waveguide QED platforms.