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Multimode-cavity picture of non-Markovian waveguide QED

Dario Cilluffo1,*, Luca Ferialdi2, G. Massimo Palma2, Giuseppe Calajò3, and Francesco Ciccarello2

  • *Contact author: dario.cilluffo@uni-ulm.de
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Phys. Rev. Research 8, 023172 – Published 18 May, 2026

DOI: https://doi.org/10.1103/hc4r-2st8

Abstract

We introduce a picture to describe and interpret waveguide-QED problems in the non-Markovian regime of long photonic retardation times resulting in delayed coherent feedback. The framework is based on an intuitive spatial decomposition of the waveguide into blocks. Among these, the block directly coupled to the atoms embodies an effective lossy multimode cavity leaking into the rest of the waveguide, in turn embodying an effective white-noise bath. The dynamics can be approximated by retaining only a finite number of cavity modes, which grows with the time delay. This description captures the atomic as well as the field’s dynamics, even with many excitations, in both emission and scattering processes. As an application, we show that the recently identified non-Markovian steady states can be understood by retaining very few or even only one cavity mode.

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Phys. Rev. Research 8, 023172– Published 18 May, 2026
  • Received 30 April 2024
  • Revised 18 August 2025
  • Accepted 4 March 2026
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