Single-photon scattering by a giant molecule asymmetrically coupled to parallel waveguides

TL;DR

This paper explores how a giant molecule coupled to parallel waveguides can be engineered to control single-photon routing through interference effects, atomic detuning, and non-Markovian dynamics.

Contribution

It introduces a comprehensive analysis of photon scattering in a giant molecule system, highlighting the roles of asymmetry, detuning, and retardation in photon routing.

Findings

Asymmetry and detuning enable control over resonance splitting.

Retardation effects reshape spectra and induce transitions between coupling regimes.

Multiple resonances and avoided crossings emerge with long time delays.

Abstract

We investigate single-photon scattering in a waveguide-QED setup, where a giant molecule composed of two frequency-detuned giant atoms is coupled to two parallel waveguides via multiple connection points. The competition between coherent atom--atom coupling and the effective decay rates dictates the splitting of a single resonance into a doublet in the transmission (reflection) spectra. By tailoring the asymmetry of the decay rates and the atomic detuning, one can engineer photon-path interference to optimize the transfer between waveguides; under chiral coupling conditions, this interference can be further harnessed to realize fully deterministic routing. In the non-Markovian regime, retardation effects can reshape the spectra and actively drive transitions between the weak- and strong-coupling regimes, converting an unsplit Markovian resonance into a clearly separated doublet, or conversely merging a split doublet back into a single resonance. For sufficiently long time delays, it further generates multiple resonances and avoided crossings, enriching the spectral response. Our results demonstrate how atomic detuning, decay-rate asymmetry, and non-Markovian retardation cooperate to provide versatile, interference-based control over single-photon routing in multi-port quantum networks.