Flat band mediated photon-photon interactions in 2D waveguide QED networks

TL;DR

This paper demonstrates how a 2D waveguide QED network with a Lieb lattice supports flat bands enabling localized photon states and explores photon interactions and transport in different regimes, revealing potential for correlated photonic states.

Contribution

It introduces a flat band in a 2D waveguide QED system and analyzes photon interactions and dynamics in softcore and hardcore regimes, revealing new correlated photon phenomena.

Findings

Flat band supports localized photon states despite long-range couplings.

Interaction-induced photon transport occurs via bound photon pairs in the softcore regime.

Metastable exciton-like states emerge in the hardcore regime involving flat and dispersive bands.

Abstract

We investigate a Lieb lattice of quantum emitters coupled to a two-dimensional waveguide network and demonstrate that this system supports an energetically isolated flat band, enabling localization despite the presence of long-range photon-mediated couplings. We then explore the two-excitation dynamics in both the softcore and hardcore interaction regimes, which arise from the nonlinearity of the emitters. In the softcore regime, we observe interaction-induced photon transport within the flat band, mediated by the formation of bound photon pairs. In the hardcore regime, corresponding to the two-level atom limit, we instead find the emergence of metastable exciton-like dressed states involving both flat and dispersive bands. Our findings highlight how the interplay between the collective behavior of emitters and effective photon-photon interactions can provide a platform for studying highly correlated photonic states in flat-band systems.