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arxiv: 2606.02440 · v1 · pith:7FVF6IAXnew · submitted 2026-06-01 · 🪐 quant-ph

Microwave Crosstalk in Planar Superconducting Quantum Devices

Yongxin Song , Dominic Hagmann , Kieran Dalton , Felix Henrich , Felix Wagner , Mohsen Bahrami Panah , Marek Pechal , Andreas Wallraff This is my paper

Pith reviewed 2026-06-28 14:30 UTC · model grok-4.3

classification 🪐 quant-ph
keywords microwave crosstalksuperconducting qubitsplanar devicesair bridgesdrive linesquantum control errorsdevice layoutcrosstalk modeling
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The pith

Physical models quantitatively explain microwave crosstalk from drive lines near qubits and air-bridge crossovers in superconducting devices.

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

The paper sets out to demonstrate that two specific device geometries produce strong microwave crosstalk and that electromagnetic models of those geometries can match the measured values in fabricated planar superconducting circuits. This matters for scaling because crosstalk creates control errors that accumulate across many qubits. The authors fabricate and measure test structures featuring a drive line routed near another qubit and a drive line crossing a coupler via an air bridge, then show that their models reproduce the experimental crosstalk amplitudes. From the agreement they extract design rules for lowering crosstalk. A sympathetic reader sees this as supplying usable layout guidance that addresses a known barrier to larger quantum processors.

Core claim

We identify two structures that can lead to strong crosstalk: a drive line routed in close proximity to another qubit, and a drive line crossing a qubit-qubit coupler using an air bridge. We design and characterize devices involving these structures and develop physical models that quantitatively explain the experimentally observed crosstalk. Based on these models, we discuss the design considerations for reducing microwave crosstalk, providing practical guidance for low-crosstalk device layouts.

What carries the argument

Electromagnetic coupling models for the two identified geometries (drive-line proximity and air-bridge crossover)

If this is right

  • Avoiding close routing of drive lines to qubits lowers crosstalk.
  • Reducing coupling at air-bridge crossovers over couplers decreases control errors.
  • Layout choices informed by the models improve overall device fidelity.
  • Once these dominant sources are controlled, weaker crosstalk mechanisms can be isolated and studied.

Where Pith is reading between the lines

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

  • The same modeling approach could be applied to predict crosstalk in larger arrays with more complex routing networks.
  • Geometric effects identified here may appear in other microwave-controlled platforms beyond planar superconductors.
  • Embedding the models in automated layout software would allow rapid screening of candidate designs for low crosstalk.
  • Varying bridge height or lateral spacing in follow-up devices would test how sensitive the predictions are to fabrication tolerances.

Load-bearing premise

The measured crosstalk is dominated by the two identified geometric structures and that no other uncharacterized mechanisms contribute significantly to the observed values.

What would settle it

A device containing one of the two structures in which the measured crosstalk deviates substantially from the quantitative prediction of the corresponding physical model.

Figures

Figures reproduced from arXiv: 2606.02440 by Andreas Wallraff, Dominic Hagmann, Felix Henrich, Felix Wagner, Kieran Dalton, Marek Pechal, Mohsen Bahrami Panah, Yongxin Song.

Figure 1
Figure 1. Figure 1: b. We refer to this mechanism as crossover-induced crosstalk. Despite being a second-order effect, crossover￾induced crosstalk can be the most prominent crosstalk source on planar devices due to the considerable cross￾capacitance and large capacitor pads used to realize sig￾nificant qubit-qubit couplings. In Sec. V, we discuss the measurement of a test structure where a drive line crosses a static qubit-qu… view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2 [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3 [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4 [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5 [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6 [PITH_FULL_IMAGE:figures/full_fig_p007_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: FIG. 7 [PITH_FULL_IMAGE:figures/full_fig_p009_7.png] view at source ↗
Figure 9
Figure 9. Figure 9: FIG. 9 [PITH_FULL_IMAGE:figures/full_fig_p010_9.png] view at source ↗
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Figure 10. Figure 10: FIG. 10 [PITH_FULL_IMAGE:figures/full_fig_p011_10.png] view at source ↗
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Figure 11. Figure 11: FIG. 11 [PITH_FULL_IMAGE:figures/full_fig_p012_11.png] view at source ↗
Figure 14
Figure 14. Figure 14: FIG. 14 [PITH_FULL_IMAGE:figures/full_fig_p013_14.png] view at source ↗
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Figure 13. Figure 13: FIG. 13 [PITH_FULL_IMAGE:figures/full_fig_p013_13.png] view at source ↗
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Figure 15. Figure 15: FIG. 15 [PITH_FULL_IMAGE:figures/full_fig_p014_15.png] view at source ↗
read the original abstract

Microwave crosstalk poses a major challenge to scaling superconducting quantum devices as it introduces excess control errors. Although its magnitude and impact have been explored in various experimental settings, quantitative physical models capable of explaining measured crosstalk for a given device geometry remain scarce. Here, we address this gap by investigating microwave crosstalk in planar superconducting devices with crossovers. We identify two structures that can lead to strong crosstalk: a drive line routed in close proximity to another qubit, and a drive line crossing a qubit-qubit coupler using an air bridge. We design and characterize devices involving these structures and develop physical models that quantitatively explain the experimentally observed crosstalk. Based on these models, we discuss the design considerations for reducing microwave crosstalk. Our results provide practical guidance for low-crosstalk device layouts and establish a basis for the systematic investigation of weaker crosstalk mechanisms.

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 two geometric structures in planar superconducting quantum devices—a drive line routed near another qubit and a drive line crossing a qubit-qubit coupler via an air bridge—produce strong microwave crosstalk, and that physical models of these structures quantitatively explain the experimentally observed crosstalk values in the tested devices. The work characterizes devices incorporating these structures and offers design considerations for crosstalk reduction.

Significance. If the models are shown to be predictive with proper isolation of mechanisms and validation statistics, the results would provide practical value for low-crosstalk layouts in scaling superconducting quantum processors, addressing a key source of control errors. The combination of targeted device design and physical modeling could establish a template for studying additional crosstalk channels.

major comments (2)
  1. [Device Design and Characterization] The manuscript designs and measures devices that include the two identified structures but does not report control devices that exclude both structures while holding all other layout, fabrication, and packaging parameters fixed. Without such controls or explicit upper bounds on residual crosstalk from other sources (substrate modes, packaging, etc.), it is not possible to confirm that the modeled terms dominate the measured values rather than uncharacterized parallel paths.
  2. [Abstract and Modeling] Abstract and model sections: the claim of quantitative agreement between models and data is asserted, yet the provided text supplies no details on model derivation from first principles, number of free parameters, error bars on measurements or predictions, or statistical measures of fit quality (e.g., reduced chi-squared). This information is load-bearing for evaluating whether the agreement is non-trivial.
minor comments (2)
  1. [Abstract] The abstract would benefit from inclusion of at least one concrete quantitative result (e.g., measured vs. modeled crosstalk in dB at a specific frequency) to allow readers to gauge the strength of the agreement immediately.
  2. [Modeling] Notation for the physical models (e.g., definitions of capacitances or inductances used in the crosstalk calculations) should be introduced with explicit equations or a table to improve readability for experimentalists.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive feedback, which highlights important aspects of experimental controls and modeling transparency. We address each major comment below and outline revisions to strengthen the manuscript.

read point-by-point responses

  1. Referee: [Device Design and Characterization] The manuscript designs and measures devices that include the two identified structures but does not report control devices that exclude both structures while holding all other layout, fabrication, and packaging parameters fixed. Without such controls or explicit upper bounds on residual crosstalk from other sources (substrate modes, packaging, etc.), it is not possible to confirm that the modeled terms dominate the measured values rather than uncharacterized parallel paths.

    Authors: We agree that dedicated control devices excluding the identified structures under identical conditions would provide stronger isolation of the crosstalk mechanisms. Fabricating such controls while maintaining all other parameters fixed presents practical challenges in our multi-qubit processor layouts. In the revised manuscript, we will add explicit upper bounds on residual crosstalk from other sources, drawing from separate measurements on devices without these structures and from literature values for substrate and packaging contributions. We will also include a dedicated discussion clarifying why the modeled terms are expected to dominate based on the observed quantitative agreement and geometry-specific scaling. revision: partial

  2. Referee: [Abstract and Modeling] Abstract and model sections: the claim of quantitative agreement between models and data is asserted, yet the provided text supplies no details on model derivation from first principles, number of free parameters, error bars on measurements or predictions, or statistical measures of fit quality (e.g., reduced chi-squared). This information is load-bearing for evaluating whether the agreement is non-trivial.

    Authors: We acknowledge that the current text lacks sufficient detail on the modeling methodology to fully substantiate the quantitative agreement. The models are based on electromagnetic finite-element simulations derived from device geometry and material properties, with a small number of free parameters (primarily effective dielectric constants). In the revision, we will expand the model sections to include step-by-step derivation outlines, reported measurement error bars (typically 0.5 dB), prediction uncertainties, and statistical fit metrics such as R^2 values. The abstract will be updated to reference these improvements where appropriate. revision: yes

Circularity Check

0 steps flagged

No circularity in derivation; models are geometry-based and externally benchmarked.

full rationale

The paper identifies two geometric structures, fabricates devices containing them, measures crosstalk, and develops physical models that quantitatively match the data. No quoted equations or steps reduce a claimed prediction to a fitted parameter by construction, invoke self-citation as the sole justification for a uniqueness theorem, or rename a known empirical pattern. The derivation chain is self-contained: device layouts are chosen, measurements are performed, and models are constructed from electromagnetic principles applied to the explicit geometries, with no load-bearing step that collapses to the input data by definition.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract-only review supplies no information on free parameters, axioms, or invented entities.

pith-pipeline@v0.9.1-grok · 5685 in / 960 out tokens · 26472 ms · 2026-06-28T14:30:38.140518+00:00 · methodology

discussion (0)

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Reference graph

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