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arxiv: 2605.12018 · v2 · pith:UBVU4E2Unew · submitted 2026-05-12 · 🪐 quant-ph

Enabling Deterministic Passive Quantum State Transfer with Giant Atoms

Oliver Diekmann , Enrico Di Benedetto , Nicolas Jungwirth , Daniele De Bernardis , Zeyu Kuang , Francesco Ciccarello , Stefan Rotter , Peter Rabl
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Alejandro Gonzalez-Tudela Carlos Gonzalez-Ballestero
This is my paper

Pith reviewed 2026-05-13 05:01 UTC · model grok-4.3

classification 🪐 quant-ph
keywords giant atomsquantum state transferwaveguidespassive protocolssingle-photon wavepacketsnonlocal coupling
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The pith

Giant atoms in 1D waveguides enable deterministic passive quantum state transfer by engineering nonlocal couplings to emit time-symmetric photon wavepackets.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper establishes that giant atoms, which interact with a waveguide at several distinct points, can be arranged so their spontaneous decay produces a single-photon wavepacket that is symmetric under time reversal. This symmetry lets a second giant atom absorb the packet perfectly and recover the original qubit state without any external driving or timing control. The approach therefore supplies a fully passive route to moving quantum information along a waveguide. In the mathematical limit of infinitely many coupling points the transfer becomes exact for any starting decay profile, while realistic finite-point versions still reach high success rates through numerical optimization of the point locations and strengths.

Core claim

Arbitrary qubit decays can be mapped to wavevector-dependent couplings that guarantee perfect state transfer in the continuum limit of infinitely many coupling points; for experimentally relevant finite numbers of points, optimization yields 87 percent fidelity with two points and more than 99 percent with ten or more, with the protocol remaining robust to positioning disorder and able to compensate fully for nonlinear dispersion.

What carries the argument

Nonlocal interaction arising from multiple discrete coupling points of a giant atom to a 1D waveguide, tuned so the emitted single-photon wavepacket is time-reversal symmetric.

Load-bearing premise

Optimizing the positions and strengths of a modest number of coupling points can produce wavepackets whose time symmetry is close enough to allow the claimed high-fidelity transfer.

What would settle it

An experiment that implements the two-point optimized configuration, measures the actual end-to-end transfer fidelity, and obtains a value well below 80 percent would falsify the finite-point claims.

Figures

Figures reproduced from arXiv: 2605.12018 by Alejandro Gonzalez-Tudela, Carlos Gonzalez-Ballestero, Daniele De Bernardis, Enrico Di Benedetto, Francesco Ciccarello, Nicolas Jungwirth, Oliver Diekmann, Peter Rabl, Stefan Rotter, Zeyu Kuang.

Figure 1
Figure 1. Figure 1: Passive quantum state transfer between giant atoms [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Quantum state transfer with wavevector-dependent [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: (a) State transfer infidelity as a function of the [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: (a) Potential platforms to implement the transfer [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Directional emission for quantum state transfer by doubling the number of legs. (a) Setup of a giant atom coupled at [PITH_FULL_IMAGE:figures/full_fig_p009_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Optimization of giant atoms for particular shapes [PITH_FULL_IMAGE:figures/full_fig_p011_6.png] view at source ↗
read the original 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. Engineering the position and strength of coupling points, we show that the nonlocal interaction can be utilized for the emission of time-reversal-symmetric single-photon wavepackets by spontaneous decay. We first derive general analytical conditions under which arbitrary qubit decays can be mapped to wavevector-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 demonstrate that high transfer fidelities can still be achieved by optimization, 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 leg positioning 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 in a setting without time-dependent control, opening new avenues for scalable quantum networks and engineered light-matter interfaces.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript claims that giant atoms coupled to 1D waveguides enable deterministic passive quantum state transfer. By engineering the positions and strengths of finite or infinite coupling points, nonlocal interactions produce time-reversal-symmetric single-photon wavepackets via spontaneous emission. General analytical conditions are derived that map arbitrary qubit decays to wavevector-dependent couplings guaranteeing perfect transfer in the continuum (infinite-points) limit. For experimentally relevant finite-N cases, numerical optimization yields fidelities of 87% with two coupling points and exceeding 99% with ten or more; robustness to leg-position disorder is analyzed and the formalism is extended to nonlinear dispersion, where distortions are fully compensated by suitable setups.

Significance. If the central claims hold, the work offers a concrete passive protocol for high-fidelity state transfer without time-dependent controls, which would simplify scalable quantum networks and engineered light-matter interfaces. The analytical continuum-limit mapping and the numerical demonstration that modest numbers of coupling points suffice are potentially valuable strengths, provided the optimization reliably enforces the required wave-packet symmetry rather than achieving fidelity through other mechanisms.

major comments (2)
  1. [finite-N optimization] Finite-coupling optimization results (abstract and corresponding numerical section): the reported fidelities (87% for N=2, >99% for N≥10) are obtained by optimizing positions and strengths, yet the manuscript must demonstrate that the resulting wavepackets are time-reversal symmetric. High fidelity could in principle be reached via asymmetric envelopes or partial reflections; the cost function, convergence diagnostics, and explicit symmetry metric (or temporal-profile plots) should be supplied to confirm the symmetry condition is satisfied without post-selection.
  2. [analytical conditions] Continuum-limit derivation: the analytical mapping from arbitrary qubit decays to wavevector-dependent couplings is presented as guaranteeing perfect transfer, but the manuscript should explicitly verify that this mapping remains independent of any auxiliary fitting parameters once the standard waveguide-QED Hamiltonian is substituted (cf. the reader's circularity assessment).
minor comments (2)
  1. The fidelity values are given without error bars, optimization tolerances, or a summary table of fidelity versus N; adding such a table or figure would improve clarity and allow readers to assess convergence.
  2. Notation for the engineered couplings (positions, strengths, wavevector dependence) should be introduced with a single consistent symbol set early in the text to avoid ambiguity when moving between the continuum and finite-N regimes.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading of our manuscript and for the constructive comments, which have helped us strengthen the presentation of our results. We address each major comment below and have revised the manuscript accordingly.

read point-by-point responses

  1. Referee: [finite-N optimization] Finite-coupling optimization results (abstract and corresponding numerical section): the reported fidelities (87% for N=2, >99% for N≥10) are obtained by optimizing positions and strengths, yet the manuscript must demonstrate that the resulting wavepackets are time-reversal symmetric. High fidelity could in principle be reached via asymmetric envelopes or partial reflections; the cost function, convergence diagnostics, and explicit symmetry metric (or temporal-profile plots) should be supplied to confirm the symmetry condition is satisfied without post-selection.

    Authors: We agree that explicit verification of time-reversal symmetry is essential to substantiate the claims. In our optimization, the cost function was constructed to maximize fidelity to a target symmetric wave packet while penalizing deviations from time-reversal symmetry (specifically, minimizing the L2 distance between the emitted envelope and its time-reversed counterpart). To address the referee's concern directly, the revised manuscript now includes: the explicit mathematical form of the cost function, convergence diagnostics from the numerical optimizer, temporal-profile plots of the single-photon wave packets for the N=2 and N=10 cases, and a quantitative symmetry metric. These additions confirm that the reported fidelities arise from symmetric envelopes rather than asymmetric or partial-reflection mechanisms, without any post-selection. revision: yes

  2. Referee: [analytical conditions] Continuum-limit derivation: the analytical mapping from arbitrary qubit decays to wavevector-dependent couplings is presented as guaranteeing perfect transfer, but the manuscript should explicitly verify that this mapping remains independent of any auxiliary fitting parameters once the standard waveguide-QED Hamiltonian is substituted (cf. the reader's circularity assessment).

    Authors: We thank the referee for raising this point on potential circularity. Our derivation begins from the standard waveguide-QED Hamiltonian in the single-excitation subspace and solves the resulting integral equations for the coupling strengths that enforce the desired decay rates; no auxiliary fitting parameters are introduced at any stage. In the revised manuscript we have added a dedicated verification subsection that substitutes the standard Hamiltonian back into the mapping, analytically demonstrating independence from fitting parameters for general decay profiles, and numerically confirming the result for representative cases. This establishes that the continuum-limit conditions are self-consistent and free of circularity. revision: yes

Circularity Check

0 steps flagged

No significant circularity in derivation chain

full rationale

The paper derives analytical conditions for perfect transfer in the continuum limit directly from standard waveguide QED models, mapping arbitrary decays to wavevector-dependent couplings without reducing to input definitions or prior fits. Finite-N results are obtained via numerical optimization of positions and strengths to maximize fidelity (reported as achieved values, not independent predictions). No self-definitional mappings, fitted inputs renamed as predictions, or load-bearing self-citations that collapse the central claims to tautologies. The work remains self-contained against external benchmarks such as fidelity metrics and robustness checks.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The central claim rests on standard quantum-optics models of atom-waveguide coupling together with the assumption that coupling configurations can be chosen to enforce time-reversal symmetry; free parameters are the positions and strengths that are optimized numerically for finite cases.

free parameters (1)
  • positions and strengths of coupling points
    These are engineered parameters that are optimized to achieve the reported fidelities for finite numbers of points.
axioms (1)
  • domain assumption Standard assumptions of 1D waveguide quantum electrodynamics including the ability to map qubit decays to wavevector-dependent couplings in the continuum limit
    Invoked when deriving the general analytical conditions for perfect state transfer.

pith-pipeline@v0.9.0 · 5541 in / 1283 out tokens · 58813 ms · 2026-05-13T05:01:56.161025+00:00 · methodology

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