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  • Open Access

Indefinite causal order in cavity quantum electrodynamics

Luis Octavio Castaños-Cervantes1, Lorenzo M. Procopio2,3,*, and Tim J. Bartley2,3

  • 1Tecnologico de Monterrey, School of Engineering and Sciences, 14380 Mexico City, Mexico
  • 2Institute for Photonic Quantum Systems (PhoQS), Paderborn University, Warburger Straße 100, 33098 Paderborn, Germany
  • 3Department of Physics, Paderborn University, Warburger Straße 100, 33098 Paderborn, Germany

  • *Contact author: lorenzo.procopio@uni-paderborn.de
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Phys. Rev. Research 8, 023295 – Published 15 June, 2026

DOI: https://doi.org/10.1103/wgr6-1g5m

Abstract

Indefinite causal order (ICO) has the potential to be a new resource for quantum information processing. In most of its experiments, ICO has been investigated in a photonic platform. Here, we investigate ICO in a cavity quantum electrodynamics system composed of two cavities. Our results show that ICO can create highly entangled states of two distant cavity fields that never interact directly independent of the initial (excited or ground) state of the atom. These entangled states can have the form of one- or two-photon NOON states. We show that ICO can interchange one photon between both cavities without changing the state of the atom, something that is impossible to achieve for two cavities in well-defined order. Furthermore, the vacuum Rabi oscillations either disappear or lose their sinusoidal form with ICO. Our results show the potential that ICO can offer in the paradigm of light-matter interaction for coherently controlling atom-field observables.

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Phys. Rev. Research 8, 023295– Published 15 June, 2026
  • Received 29 August 2025
  • Accepted 11 May 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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