Strongly Confined Atomic Excitation Localization in a Weakly-Driven Atom-Waveguide Interface

TL;DR

This paper investigates how asymmetric driving of a homogeneous atomic array coupled to a photonic crystal waveguide leads to strongly localized atomic excitations at interfaces or edges, revealing new control mechanisms for quantum states.

Contribution

It introduces a theoretical framework for asymmetric driving-induced localization in atom-waveguide systems, including empirical formulas and control methods for multi-site localization.

Findings

Localization occurs at interfaces or edges under asymmetric driving.

Size effects influence localization regimes, predictable by empirical formulas.

Defect-driving schemes enable highly confined single-site excitation localization.

Abstract

An atomic array coupled to a photonic crystal waveguide forms a strongly coupled quantum interface, exhibiting various intriguing collective features of quantum dynamics. Here we consider a homogeneous atomic array and theoretically investigate its steady-state distribution when the incident fields drive the atoms from both sides at asymmetric angles. This effectively creates an interface shared by two zones of atoms under different driving angles. This setup introduces a competition between photon-mediated dipole-dipole interactions and the directionality of coupling, while differences of the travelling phases from the incident angles further influence the overall steady-state behavior. Under this asymmetric driving scheme, the presence of strongly confined localization can be identified, where localization can occur either at the interface or at one of edges. Additionally, we examine the size effect on the atomic localization, deriving an empirical formula to predict parameter regimes that favor interfaced localization. We also consider a defect-driving scheme, where a third zone is created by undriven atoms under symmetric travelling phases. This results in strongly confined single-site excitation localization, which can be explained through analytical solutions under the reciprocal coupling. Finally, we propose several methods for precise control of multiple single-site localizations under the defect-driving scheme. Our results provide insights into driven-dissipative quantum systems with nonreciprocal couplings and pave the way for quantum simulation of exotic many-body states relevant to quantum information applications.