Controlling Excitation Localization in Waveguide QED Systems

TL;DR

This paper explores how geometry and disorder influence excitation localization in waveguide QED systems, revealing mechanisms for long-lived quantum states through spectral analysis and simulations.

Contribution

It introduces a comprehensive analysis of localization mechanisms in waveguide QED, highlighting the roles of geometry and disorder in controlling excitation dynamics.

Findings

Geometry-induced subradiance enables long-lived modes without disorder.

Disorder causes Anderson-like localization by breaking symmetry.

Transition between geometric and disorder regimes is characterized.

Abstract

We theoretically investigate excitation dynamics in one-dimensional arrays of quantum emitters coupled to a waveguide, focusing on localization and long-time population trapping. By combining time-domain simulations with spectral analysis of an effective non-Hermitian Hamiltonian, we identify two distinct mechanisms that give rise to localization: geometry-induced subradiance and disorder-induced Anderson-like confinement. Spatially modulated emitter arrangements--such as single- and double-Gaussian transverse profiles--enable long-lived subradiant modes even in the absence of disorder, with decay rates that can be finely controlled via geometric parameters. In contrast, localization in uniform arrays emerges only when disorder breaks spatial symmetry and suppresses collective emission through interference. We track the crossover between geometric and disorder-induced regimes, finding that double-Gaussian profiles exhibit clear spatial signatures of this transition, while single-Gaussian configurations display more gradual changes. These results establish geometry and disorder as complementary tools for engineering long-lived quantum states in waveguide QED systems, with direct relevance for scalable implementations in photonic platforms.