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arxiv: 2607.00172 · v2 · pith:Y3Y4LRAC · submitted 2026-06-30 · quant-ph · cond-mat.mes-hall· cond-mat.supr-con

Superconducting Spiral Inductors for RF Reflectometry: Operation at Elevated Temperatures and Magnetic Fields

Euan Parry , Murat Cubukcu , Patrick Reuvekamp , Manoj Stanley , Jonathan D. Fletcher , Alessandro Rossi This is my paper

Reviewed by Pith2026-07-02 18:38 UTCgrok-4.3pith:Y3Y4LRACopen to challenge →

classification quant-ph cond-mat.mes-hallcond-mat.supr-con
keywords superconducting spiral inductorsNbTiNRF reflectometryspin qubitselevated temperaturemagnetic fieldsresonator measurementsinductance extraction
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The pith

NbTiN spiral inductors for RF reflectometry separate inductive and capacitive effects to operate at several kelvin and fields up to 1 T.

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

The paper examines the performance of superconducting spiral inductors under conditions of several kelvin and magnetic fields approaching 1 T, conditions expected for scalable quantum computing architectures. It combines weakly coupled resonator measurements with independent two-port inductance extraction to distinguish inductive from capacitive contributions to observed changes in resonance and quality factor. This separation identifies the sources of performance shifts and yields practical design metrics that connect device geometry to temperature sensitivity and magnetic-field robustness. A sympathetic reader would care because these inductors support readout of semiconductor spin qubits, and metrics for stable operation at higher temperatures and fields could simplify hardware requirements for future quantum processors.

Core claim

Superconducting spiral inductors made from NbTiN remain functional for RF reflectometry at temperatures of several kelvin and magnetic fields approaching 1 T. By combining weakly coupled resonator measurements with independent two-port inductance extraction, the work separates inductive and capacitive contributions to device behaviour and directly identifies the origin of resonance shifts and quality factor degradation. This leads to practical design metrics linking geometry, temperature sensitivity, and magnetic-field robustness, providing a framework for benchmarking superconducting inductors and guiding the design of future RF-reflectometry circuits.

What carries the argument

Dual measurement approach that combines weakly coupled resonator measurements with two-port inductance extraction to isolate inductive and capacitive contributions.

If this is right

  • Design metrics connect inductor geometry directly to temperature sensitivity and magnetic-field robustness.
  • Resonance shifts and quality factor degradation are traceable to specific inductive or capacitive origins.
  • A general benchmarking framework is established for superconducting inductors in RF-reflectometry applications.
  • Geometry choices can be used to reduce performance degradation at elevated temperatures and fields.

Where Pith is reading between the lines

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

  • The separation technique could be applied to diagnose performance limits in other superconducting RF components used with quantum devices.
  • Metrics derived here could guide selection of inductor dimensions for circuits intended to operate without millikelvin cooling.
  • The same dual-measurement strategy might reveal whether similar inductive-capacitive separation holds for different superconductor materials.

Load-bearing premise

The two measurement techniques cleanly isolate inductive versus capacitive effects with negligible cross-talk or unmodeled losses under the tested temperature and field ranges.

What would settle it

If two-port inductance values extracted from the same devices fail to quantitatively account for the resonance frequency shifts measured in the weakly coupled resonator setup, that mismatch would show the separation of effects is incomplete.

Figures

Figures reproduced from arXiv: 2607.00172 by Alessandro Rossi, Euan Parry, Jonathan D. Fletcher, Manoj Stanley, Murat Cubukcu, Patrick Reuvekamp.

Figure 1
Figure 1. Figure 1: Parallel configuration tank circuit for gate-based [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Device geometry and microwave characterisation [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: (a) L(T) extracted from the bonded two-port measurements of D2 carried out in set-up 2 (blue circles) and f0(T) extracted from the inductively coupled notch measurements of a nominally identical D2 device carried out in set-up 1 (orange circles). The blue dashed line is the fit discussed in Section III and gives Lg = 106 nH, within 3% of the designed value, and Lk,□ = 1.74 pH/sq. The orange dashed line sho… view at source ↗
Figure 4
Figure 4. Figure 4: Temperature- and field-dependent quality factor degradation. (a) [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Design metrics. (a) Fractional frequency shift between 2 K and 8 K as a function of kinetic-inductance fraction [PITH_FULL_IMAGE:figures/full_fig_p007_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Amplitude of S-parameter response as a function of [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Two-point DC resistance measurement as a func [PITH_FULL_IMAGE:figures/full_fig_p009_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Calculated minimum outer spiral diameter re [PITH_FULL_IMAGE:figures/full_fig_p010_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Temperature and magnetic-field dependence of [PITH_FULL_IMAGE:figures/full_fig_p011_9.png] view at source ↗
read the original abstract

Superconducting spiral inductors are emerging as key components for radio-frequency (RF) reflectometry, a widely used readout technique for semiconductor spin qubits. Future scalable quantum-computing architectures are expected to operate at elevated temperatures and magnetic fields, placing new demands on the performance and stability of superconducting circuit elements. Here, we present a systematic study of NbTiN spiral inductors under temperatures of several kelvin and magnetic fields approaching 1 T. By combining weakly coupled resonator measurements with independent two-port inductance extraction, we separate inductive and capacitive contributions to device behaviour and directly identify the origin of resonance shifts and quality factor degradation. Furthermore, we establish practical design metrics linking geometry, temperature sensitivity, and magnetic-field robustness. These results provide a general framework for benchmarking superconducting inductors and guiding the design of future RF-reflectometry circuits for practical quantum technologies.

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

0 major / 2 minor

Summary. The manuscript presents a systematic experimental study of NbTiN superconducting spiral inductors intended for RF reflectometry readout of semiconductor spin qubits. The central claim is that combining weakly coupled resonator measurements with independent two-port inductance extraction cleanly separates inductive and capacitive contributions to device behavior, thereby identifying the physical origins of resonance shifts and quality-factor degradation at temperatures of several kelvin and magnetic fields approaching 1 T; the work also derives practical design metrics that link inductor geometry to temperature sensitivity and magnetic-field robustness, supplying a general benchmarking framework for future RF-reflectometry circuits.

Significance. If the claimed separation of inductive and capacitive effects is experimentally validated with negligible cross-talk, the results would supply concrete, geometry-dependent guidelines for operating superconducting inductors under the elevated-temperature and moderate-field conditions expected in scalable quantum-computing architectures. The provision of reproducible measurement protocols and design metrics constitutes a practical contribution to the field.

minor comments (2)
  1. The abstract states that the two techniques 'directly identify the origin' of shifts and Q degradation, but the manuscript should explicitly quantify the residual cross-talk or unmodeled losses between the weakly-coupled-resonator and two-port methods (e.g., via a dedicated error-budget subsection or supplementary table) to substantiate the claim of clean separation.
  2. Figure captions and axis labels should include the precise temperature and field values at which each data set was acquired, together with the number of devices measured, to allow readers to assess statistical robustness.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive summary of the work and the recommendation for minor revision. No major comments were provided in the report.

Circularity Check

0 steps flagged

No significant circularity

full rationale

This is an experimental measurement paper on NbTiN spiral inductors using standard RF techniques (weakly coupled resonators and two-port extraction). The central claims concern empirical separation of inductive vs. capacitive effects and design metrics derived from temperature/field data. No derivation chain, equations, fitted parameters renamed as predictions, or self-citation load-bearing steps are present. The results are directly tied to measured data without reduction to inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Only the abstract is available; no explicit free parameters, ad-hoc axioms, or invented entities are stated. Standard assumptions of RF circuit metrology and superconductivity are implicit but not detailed.

axioms (1)
  • domain assumption Standard assumptions of RF circuit metrology and superconductivity hold for the tested devices.
    Implicit in the experimental description; location: abstract.

pith-pipeline@v0.9.1-grok · 5700 in / 1201 out tokens · 27115 ms · 2026-07-02T18:38:44.959763+00:00 · methodology

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