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Enabling Deterministic Passive Quantum State Transfer with Giant Atoms

Oliver Diekmann1, Enrico Di Benedetto2, Nicolas Jungwirth3,4,5,‡, Daniele De Bernardis6,9, Zeyu Kuang1, Francesco Ciccarello2, Stefan Rotter1, Peter Rabl3,4,5, Alejandro González-Tudela7,8,* et al.

Carlos Gonzalez-Ballestero1,†

  • *Contact author: a.gonzalez.tudela@csic.es
  • †Contact author: carlos.gonzalez-ballestero@tuwien.ac.at
  • ‡Present address: Institut für Experimentalphysik, Universität Innsbruck, Technikerstraße 25/4, 6020 Innsbruck, Austria.
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PRX Quantum 7, 043013 – Published 20 October, 2026

DOI: https://doi.org/10.1103/6wcb-nj42

Abstract

Achieving quantum state transfer in passive ways can become a powerful asset for scalable quantum networks. Here, we demonstrate how giant atoms coupled to 1D waveguides provide a platform for such a passive, deterministic transfer. Specifically, we show that when the giant atom’s extent is comparable to the width of the emitted wave packet, this wave packet can be designed to be time-reversal-symmetric by engineering the positions and strengths of atom-waveguide coupling points. We first derive general analytical conditions under which arbitrary qubit decays can be mapped to wave-vector-dependent couplings that guarantee perfect state transfer in the continuum limit of infinitely many coupling points. Then, for experimentally relevant configurations with a finite number of coupling points, we optimize the coupling positions and values. We demonstrate that the transfer fidelity can be boosted well beyond the value for a single coupling point (54%), reaching 87% with only two coupling points and exceeding 99% with ten or more. We further analyze the robustness of the protocol against disorder in the coupling points as well as frequency variations of the qubits and extend the formalism to environments with nonlinear dispersion, showing that dispersion-induced distortions can be fully compensated by judiciously chosen setups. Our results establish giant atoms as a powerful platform for realizing high-fidelity quantum state transfer and demonstrate how time-dependent control can be instead encoded into the device design.

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Popular Summary

Passing quantum information between distant nodes usually demands precise time-dependent control to shape how a photon is emitted and caught. Here, we show that the necessary photon shape can be built into the hardware itself using “giant atoms,” which interact with a waveguide at several points. By carefully arranging the giant atom’s connection points, it naturally releases a photon wave packet with the right symmetric shape to be perfectly absorbed by a second atom, without the need for external control. We analytically prove that this can be achieved very generally and show that simple, realistic designs already reach near-perfect performance. The method is robust and works even in more complex settings. By replacing active control with judicious spatial design, our work points toward simpler and more scalable quantum networks.

Article Text

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PRX Quantum 7, 043013– Published 20 October, 2026
  • Received 12 May 2026
  • Revised 6 August 2026
  • Accepted 14 September 2026
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