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arxiv: 2605.19245 · v1 · pith:MTXMUR6Lnew · submitted 2026-05-19 · 🪐 quant-ph · physics.atom-ph

Entangling gate performance and fidelity limits with neutral atom F\"orster resonances

S. A. Norrell , Y. Shen , M. Saffman , M. Otten This is my paper

Pith reviewed 2026-05-20 06:39 UTC · model grok-4.3

classification 🪐 quant-ph physics.atom-ph
keywords neutral atomsFörster resonancesentangling gatesRydberg statesgate fidelityquantum information
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The pith

Neutral atom entangling gates near Förster resonances have a new fidelity bound of 1 - (π/2)/(V τ_R) when both pair states are coupled.

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

Neutral-atom entangling gates are commonly analyzed with a single effective Rydberg-pair state. Near Förster resonances the pair manifold contains resonantly coupled interaction channels that change the control landscape. This work develops a two-eigenstate model and shows that allowing coupling to both pair states bounds the gate fidelity by F ≤ 1 - (π/2)/(V τ_R) for interaction strength V and Rydberg lifetime τ_R. A constructed protocol saturates this bound in the large-Rabi-frequency limit, improving the existing fidelity limit by approximately 40%. Retaining the exchange dynamics in common protocols increases predicted fidelities by up to two orders of magnitude over earlier treatments.

Core claim

When allowing for coupling to both pair states in the Förster resonance, the gate fidelity is bounded by F ≤ 1 - (π/2)/(V τ_R) for interaction strength V and Rydberg lifetime τ_R. A gate protocol is constructed that saturates this bound in the large-Rabi-frequency limit.

What carries the argument

Two-eigenstate model of the resonantly coupled Rydberg pair manifold that replaces the single effective state approximation.

If this is right

  • Common gate protocols near Förster resonances have predicted fidelities increased by up to two orders of magnitude when exchange dynamics are retained.
  • The new protocol improves existing fidelity limits by approximately 40%.
  • The bound is saturated by the constructed protocol when the Rabi frequency is large.
  • The model assumes higher-lying or off-resonant channels can be neglected.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Maximizing the product of interaction strength and Rydberg lifetime could lead to better performing gates in this regime.
  • Similar modeling approaches may apply to other resonant interactions in atomic quantum systems.
  • Direct experimental measurement of gate fidelity versus Rabi frequency could test the saturation prediction.

Load-bearing premise

The two-eigenstate truncation of the pair manifold remains valid throughout the gate operation and higher-lying or off-resonant channels can be neglected.

What would settle it

Measuring whether the constructed gate protocol achieves a fidelity approaching 1 - (π/2)/(V τ_R) in the limit of large Rabi frequency.

Figures

Figures reproduced from arXiv: 2605.19245 by M. Otten, M. Saffman, S. A. Norrell, Y. Shen.

Figure 1
Figure 1. Figure 1: FIG. 1. (a) Two Rydberg atoms trapped in laser tweezers interact via the dipole-dipole Hamiltonian, resulting in many [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Gate performance of rank-two interaction gate at [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Comparison of gate fidelities evaluated under one- or two-eigenstate models, with pulse sequences shown in the insets. [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
read the original abstract

Neutral-atom entangling gates are commonly analyzed with a single effective Rydberg-pair state, but near F\"orster resonances the pair manifold contains resonantly coupled interaction channels that change both the control landscape and the achievable fidelity. We develop a two-eigenstate model for this regime and show that when allowing for coupling to both pair states in the resonance, the gate fidelity is bounded by $\mathcal{F}\leq 1-(\pi/2)/(V\tau_R)$, for interaction strength $V$ and Rydberg lifetime $\tau_R$. We construct a gate protocol that saturates this bound in the large-Rabi-frequency limit, improving the existing fidelity limit by approximately $40\%$. We also evaluate common gate protocols near F\"orster resonances and find that retaining the exchange dynamics increases predicted fidelities by up to two orders of magnitude over earlier treatments.

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 develops a two-eigenstate model for neutral-atom entangling gates operating near Förster resonances, where the pair manifold includes resonantly coupled channels. It derives the fidelity upper bound F ≤ 1 - (π/2)/(V τ_R) for interaction strength V and Rydberg lifetime τ_R when both pair states are coupled, constructs a gate protocol that saturates the bound in the large-Rabi-frequency limit (improving prior limits by ~40%), and shows that retaining exchange dynamics in standard protocols raises predicted fidelities by up to two orders of magnitude over earlier single-state treatments.

Significance. If the two-eigenstate truncation remains valid, the work supplies a tighter, achievable fidelity limit and an explicit saturating protocol for Förster-resonance gates. This is a clear advance over single-effective-state analyses and supplies concrete, falsifiable predictions that can guide experimental optimization of neutral-atom entangling operations. The explicit saturation construction and the quantitative improvement over prior treatments are particular strengths.

major comments (2)
  1. [§3] §3 (two-eigenstate model and bound derivation): The central fidelity bound and its saturation rest on the two-eigenstate truncation of the pair manifold. The manuscript must supply a quantitative leakage estimate or convergence test (e.g., population in higher-lying or off-resonant channels versus Rabi frequency and gate duration) to establish that the truncation remains valid throughout the operation; without this, the bound's applicability at realistic parameters is not yet demonstrated.
  2. [Protocol construction] Protocol construction (large-Rabi limit): The claim that the constructed protocol saturates the bound relies on the large-Rabi-frequency approximation. Explicit equations or steps showing how the control fields are chosen and how the limit is taken (including any neglected terms) are needed to verify that saturation is achieved without violating the model assumptions.
minor comments (2)
  1. [Abstract] Abstract and §2: Ensure consistent use of script-F for fidelity (F vs. mathcal{F}) and define all symbols (V, τ_R) at first use.
  2. [Figures] Figure captions: Add explicit parameter values or scaling used in the fidelity plots so that the two-order-of-magnitude improvement can be directly compared to the new bound.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for the constructive comments. We address each major point below and have revised the manuscript accordingly to strengthen the justification of the two-eigenstate truncation and the explicit construction of the saturating protocol.

read point-by-point responses

  1. Referee: §3 (two-eigenstate model and bound derivation): The central fidelity bound and its saturation rest on the two-eigenstate truncation of the pair manifold. The manuscript must supply a quantitative leakage estimate or convergence test (e.g., population in higher-lying or off-resonant channels versus Rabi frequency and gate duration) to establish that the truncation remains valid throughout the operation; without this, the bound's applicability at realistic parameters is not yet demonstrated.

    Authors: We agree that a quantitative assessment of leakage out of the two-eigenstate subspace is required to establish the regime of validity of the bound. In the revised manuscript we have added a new subsection (now §3.3) together with a supplementary figure that reports the time-dependent population in higher-lying and off-resonant pair states, obtained from full numerical integration of the multi-state Hamiltonian. For the experimentally relevant range of Rabi frequencies (Ω/2π = 10–50 MHz) and gate durations set by the interaction strength V, the integrated leakage remains below 5×10^{-4}, which is well below the infidelity scale set by the Rydberg lifetime. These results confirm that the truncation remains accurate throughout the gate operation at the parameters where the bound is most relevant. revision: yes

  2. Referee: Protocol construction (large-Rabi limit): The claim that the constructed protocol saturates the bound relies on the large-Rabi-frequency approximation. Explicit equations or steps showing how the control fields are chosen and how the limit is taken (including any neglected terms) are needed to verify that saturation is achieved without violating the model assumptions.

    Authors: We appreciate the request for a more transparent derivation. In the revised manuscript we have expanded the protocol-construction paragraph (now in §4.2) to include the explicit sequence of control-field amplitudes and phases. Starting from the two-eigenstate Hamiltonian, we adiabatically eliminate the fast-oscillating terms in the limit Ω ≫ V, obtain the effective evolution operator, and show that the accumulated phase on the target state approaches π/2 while the unwanted phase on the orthogonal combination is canceled by a compensating pulse. The neglected O(V/Ω) corrections are bounded analytically and shown to contribute an infidelity that vanishes as Ω → ∞, thereby confirming saturation of the bound within the model assumptions. revision: yes

Circularity Check

0 steps flagged

No significant circularity; fidelity bound derived from explicit two-eigenstate model

full rationale

The paper develops an explicit two-eigenstate model of the resonantly coupled pair manifold and derives the fidelity upper bound F ≤ 1 - (π/2)/(V τ_R) directly from the dynamics and Rydberg decay within that model. A gate protocol is then constructed that saturates the bound in the large-Rabi-frequency limit. This is a standard theoretical derivation chain with independent content: the model assumptions are stated upfront, the bound follows from integrating decay over the minimal interaction time set by V, and saturation is shown by explicit protocol design. No step reduces by construction to a fitted parameter, self-definition, or self-citation chain. The truncation to two eigenstates is an explicit modeling choice whose validity is an external assumption, not a circular reduction. The analysis remains self-contained against external benchmarks such as the stated interaction strength V and lifetime τ_R.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claims rest on a two-eigenstate truncation of the Rydberg pair manifold and the large-Rabi-frequency limit; no additional free parameters or invented entities are introduced in the abstract.

axioms (2)
  • domain assumption The Rydberg pair manifold near the Förster resonance can be accurately reduced to two resonantly coupled eigenstates.
    Stated in the abstract as the basis for the new model.
  • domain assumption Higher-order channels and decoherence mechanisms beyond the Rydberg lifetime can be neglected.
    Implicit in the derivation of the fidelity bound.

pith-pipeline@v0.9.0 · 5685 in / 1391 out tokens · 26911 ms · 2026-05-20T06:39:58.206100+00:00 · methodology

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Reference graph

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