arxiv: 2604.02809 · v1 · submitted 2026-04-03 · 🪐 quant-ph

Recognition: 1 theorem link

· Lean Theorem

Characterizing charge-parity detection based on an offset-charge-tunable transmon qubit via randomized benchmarking

Yao-Yao Jiang , Tang Su , Yuxiang Liu , Yi-Ming Guo , Yidong Song , Yu-Long Li , Yanjie Zeng , Guang-Ming Xue

show 6 more authors

Wei-Jie Sun Mei-Ling Li Yi-Rong Jin Junhua Wang Xuegang Li Hai-Feng Yu

Authors on Pith no claims yet

Pith reviewed 2026-05-13 20:12 UTC · model grok-4.3

classification 🪐 quant-ph

keywords charge-parity detectionoffset-charge-tunable transmonrandomized benchmarkingsuperconducting qubitnet-zero pulsespin-echo sequencefidelity characterizationcontinuous monitoring

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The pith

An offset-charge-tunable transmon qubit maps charge-parity states to qubit states at 99.37 percent fidelity.

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

This paper shows how an offset-charge-tunable transmon qubit can map charge-parity states onto the qubit's computational states. A gate control line tunes the offset charge, and a net-zero pulse combined with a spin-echo sequence performs the mapping. Randomized benchmarking then measures the detection fidelity at 99.37 percent, while continuous monitoring reaches over 93.4 percent fidelity at a 4 microsecond sampling interval. Error analysis identifies qubit readout as the dominant source of error. The setup is presented as a step toward detecting rare low-energy events on the meV scale.

Core claim

Using an offset-charge-tunable transmon qubit, the authors achieve high-fidelity mapping of charge-parity states onto qubit states. A gate control line controls the offset charge to reach single-qubit gate fidelity of 99.96 percent. Combining a net-zero-based pulse on the gate line with a spin-echo-based sequence realizes the charge-parity mapping at 99.37 percent fidelity as measured by randomized benchmarking. Continuous monitoring is demonstrated with over 93.4 percent fidelity at 4 microsecond intervals, and error analysis identifies qubit readout as the dominant error source.

What carries the argument

offset-charge-tunable transmon qubit using net-zero gate pulses and spin-echo sequences to map charge-parity states onto qubit states

If this is right

Single-qubit gate fidelity reaches 99.96 percent when the gate control line tunes offset charge.
Charge-parity detection fidelity reaches 99.37 percent when characterized by randomized benchmarking.
Continuous charge-parity monitoring exceeds 93.4 percent fidelity at 4 microsecond intervals.
Qubit readout remains the largest error source in the charge-parity detection process.
The demonstrated mapping provides a concrete foundation for exploring ultra-low energy particles.

Where Pith is reading between the lines

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

The same mapping technique could support searches for rare events such as low-energy dark matter interactions at meV scales.
Reducing readout infidelity would directly raise the overall charge-parity fidelity above the current 99.37 percent limit.
The approach may transfer to other tunable superconducting qubits to improve real-time charge sensing in larger circuits.
Integration into quantum processors could enable built-in monitoring of environmental charge fluctuations during computation.

Load-bearing premise

The net-zero pulse on the gate line combined with the spin-echo sequence maps charge parity faithfully without introducing uncontrolled decoherence or offset-charge drift.

What would settle it

An independent calibration that injects known charge-parity states and measures detection outcomes below 99 percent fidelity would disprove the reported mapping accuracy.

Figures

Figures reproduced from arXiv: 2604.02809 by Guang-Ming Xue, Hai-Feng Yu, Junhua Wang, Mei-Ling Li, Tang Su, Wei-Jie Sun, Xuegang Li, Yanjie Zeng, Yao-Yao Jiang, Yidong Song, Yi-Ming Guo, Yi-Rong Jin, Yu-Long Li, Yuxiang Liu.

**Figure 1.** Figure 1: FIG. 1. (a) False-colored optical image of a single-qubit unit in the device. The bottom chip comprises a microwave (MW) [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗

**Figure 2.** Figure 2: FIG. 2. (a) Qubit spectrum as a function of flux Φ [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗

**Figure 4.** Figure 4: FIG. 4. (a) A 1.6-ms time slice of the charge-parity detec [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗

**Figure 5.** Figure 5: FIG. 5 [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗

**Figure 6.** Figure 6: FIG. 6. Optimization of the gate-pulse duration via [PITH_FULL_IMAGE:figures/full_fig_p007_6.png] view at source ↗

**Figure 7.** Figure 7: FIG. 7. The schematic waveform of a net-zero-based gate [PITH_FULL_IMAGE:figures/full_fig_p008_7.png] view at source ↗

**Figure 9.** Figure 9: FIG. 9. Comparison of PSD between (a) Ramsey-based and [PITH_FULL_IMAGE:figures/full_fig_p009_9.png] view at source ↗

read the original abstract

Superconducting qubits are compelling platforms for charge-parity detection and, due to their theoretical sensitivity on the meV energy scale, hold promise for rare event searches. In this work, we realize high-fidelity mapping of charge-parity states onto qubit states using an offset-charge-tunable transmon qubit and efficiently characterize the fidelity of the charge-parity detection via randomized benchmarking. Specifically, a gate control line is applied to control offset charge, allowing us to achieve the single-qubit gate fidelity up to 99.96%. We combine a net-zero-based pulse on the gate line with a spin-echo-based sequence to realize charge-parity mapping, achieving a fidelity of 99.37%. Then, we demonstrate continuous monitoring of the charge-parity state with over 93.4% fidelity at a 4-\mu s sampling interval. Finally, an error analysis of charge-parity detection is performed, and it is found that qubit readout is currently the largest source of error. We believe this work lays the foundation for future exploration of ultra-low energy particles.

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.

Desk Editor's Note private letter to a colleague

They map charge parity onto a tunable transmon at 99.37% fidelity with net-zero pulses and spin-echo, then benchmark it with RB, but the numbers may overlook slow offset-charge drift.

read the letter

The core result is a working charge-parity sensor on an offset-charge-tunable transmon. They drive the gate line with a net-zero pulse inside a spin-echo sequence to map parity onto the qubit state, hit 99.37% fidelity by randomized benchmarking, and keep continuous monitoring above 93% at 4 µs intervals. Single-qubit gates reach 99.96%. Readout is identified as the dominant error. That combination of hardware and pulse sequence is the concrete advance here; it is not a new protocol but a targeted implementation that delivers usable numbers for sensing work on the meV scale.

Referee Report

1 major / 1 minor

Summary. The manuscript experimentally demonstrates high-fidelity charge-parity detection in an offset-charge-tunable transmon qubit. A net-zero pulse on the gate line combined with a spin-echo sequence maps charge-parity states onto the qubit; randomized benchmarking yields 99.96% single-qubit gate fidelity and 99.37% charge-parity mapping fidelity. Continuous parity monitoring is shown at >93.4% fidelity with 4 μs sampling, and readout is identified as the dominant error source.

Significance. If the reported mapping fidelity is robust, the work supplies a characterized, RB-efficient protocol for charge-parity detection at meV scales, directly relevant to rare-event searches with superconducting qubits. The explicit identification of readout as the limiting factor and the demonstration of continuous monitoring provide concrete guidance for device improvement.

major comments (1)

[Charge-parity mapping and RB characterization (fidelity claim of 99.37%)] The 99.37% charge-parity mapping fidelity is obtained by interleaving a net-zero gate pulse with a spin-echo sequence. No explicit verification (e.g., Ramsey visibility versus wait time or repeated parity checks over the 4 μs interval) is provided to confirm that residual offset-charge drift or extra decoherence remains negligible; without such data the RB result may overestimate the true mapping fidelity.

minor comments (1)

[Abstract and results section on RB] The abstract and main text state specific fidelity numbers but do not include raw RB survival probabilities, error budgets, or post-selection details; adding these (even in supplementary material) would allow independent assessment of the quoted values.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive comments and careful reading of our manuscript. We address the major comment below.

read point-by-point responses

Referee: [Charge-parity mapping and RB characterization (fidelity claim of 99.37%)] The 99.37% charge-parity mapping fidelity is obtained by interleaving a net-zero gate pulse with a spin-echo sequence. No explicit verification (e.g., Ramsey visibility versus wait time or repeated parity checks over the 4 μs interval) is provided to confirm that residual offset-charge drift or extra decoherence remains negligible; without such data the RB result may overestimate the true mapping fidelity.

Authors: We thank the referee for this observation. The randomized benchmarking protocol is applied directly to the full charge-parity mapping sequence (net-zero gate pulse interleaved with spin-echo), so the measured 99.37% fidelity already includes any residual offset-charge drift or decoherence present during sequence execution. The spin-echo is chosen specifically to refocus low-frequency charge noise. That said, we agree that explicit verification would strengthen the claim. In the revised manuscript we have added Ramsey visibility data versus wait time over the 4 μs interval, confirming that offset-charge drift remains negligible on these timescales and that the RB result does not overestimate the mapping fidelity. revision: yes

Circularity Check

0 steps flagged

No circularity: purely experimental characterization via direct benchmarking

full rationale

The paper reports experimental results on realizing charge-parity mapping with an offset-charge-tunable transmon and measuring its fidelity (99.37%) using randomized benchmarking. No derivation chain, first-principles prediction, or fitted parameter is presented that reduces to its own inputs by construction. The central claims rest on measured data and standard RB protocols rather than self-referential equations or load-bearing self-citations. This is the expected non-finding for an experimental characterization paper.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No mathematical model, free parameters, or axioms are stated in the abstract; the work is an experimental demonstration of fidelities.

pith-pipeline@v0.9.0 · 5544 in / 1028 out tokens · 45527 ms · 2026-05-13T20:12:50.005804+00:00 · methodology

discussion (0)

Reference graph

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