arxiv: 2604.13176 · v1 · submitted 2026-04-14 · 🪐 quant-ph · hep-ex· physics.ins-det

Measuring quasiparticle dynamics for particle impact reconstruction in a superconducting qubit chip

E. Celi , R. Linehan , P. M. Harrington , M. Li , H. D. Pinckney , K. Serniak , W. D. Oliver , J. A. Formaggio

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E. Figueroa-Feliciano D. Baxter

This is my paper

Pith reviewed 2026-05-10 15:12 UTC · model grok-4.3

classification 🪐 quant-ph hep-exphysics.ins-det

keywords quasiparticle dynamicssuperconducting qubitsparticle impact detectionphonon propagationtransmon relaxationradiation effectsenergy reconstruction

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The pith

Transmon qubits on a chip can reconstruct the energy deposited by particle impacts using correlated quasiparticle relaxation events.

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

The paper develops a statistical model for how radiation-induced quasiparticles cause qubit energy relaxation, separating recombination from trapping processes and revealing an energy-dependent relaxation rate. It then connects simultaneous relaxation events across multiple qubits to ballistic phonon travel from a single impact site. This connection supplies a localization method that extracts the deposited energy and matches Monte Carlo predictions. The result supplies a practical route for treating any collection of transmon qubits as energy-resolving particle detectors without extra hardware.

Core claim

Modeling the time evolution of radiation-induced qubit energy relaxation through quasiparticle density dynamics distinguishes recombination and trapping decay channels. Precise measurements uncover an unexpected dependence of qubit relaxation dynamics on deposited energy. Linking correlated relaxation events across qubits to ballistic phonon propagation yields a statistical localization approach that extracts the energy deposited in the substrate in good agreement with Monte Carlo simulation.

What carries the argument

Statistical localization of particle impacts from correlated qubit relaxation times, which attributes simultaneous events to ballistic phonon propagation from a single energy deposit and inverts the observed relaxation pattern to recover the deposited energy.

If this is right

Qubit relaxation can be partitioned into recombination versus trapping channels with measurable rates.
Relaxation time scales depend on the amount of energy deposited by the incident particle.
Any arbitrary subset of transmon qubits already present on a chip can function as an energy-resolving witness detector.
The extracted energies agree with Monte Carlo simulations of particle interactions in the substrate.

Where Pith is reading between the lines

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

The same qubit array could provide real-time tagging of cosmic-ray or environmental radiation events that otherwise cause correlated errors.
Energy reconstruction might allow selective reset or error-correction protocols triggered only when an impact is detected.
The approach could be tested on existing quantum processors without hardware changes by re-analyzing archived relaxation data.

Load-bearing premise

Correlated qubit relaxation events are produced by ballistic phonon propagation from one particle impact, so the statistical method can correctly recover the deposited energy.

What would settle it

A set of measured relaxation events whose spatial and temporal pattern deviates systematically from phonon-propagation predictions or whose inferred energy disagrees with independent Monte Carlo estimates of the same impacts.

Figures

Figures reproduced from arXiv: 2604.13176 by D. Baxter, E. Celi, E. Figueroa-Feliciano, H. D. Pinckney, J. A. Formaggio, K. Serniak, M. Li, P. M. Harrington, R. Linehan, W. D. Oliver.

**Figure 1.** Figure 1: FIG. 1. Probability of relaxation as a function of time after trigger as described by Eq. 1 in three different cases: [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗

**Figure 2.** Figure 2: FIG. 2. Final results of [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗

**Figure 3.** Figure 3: FIG. 3. Reconstruction of a 374 keV particle impact; [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗

**Figure 4.** Figure 4: FIG. 4. Distribution of reconstructed impacts in the chip in the [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗

**Figure 5.** Figure 5: FIG. 5. Example of real and imaginary signal components rotated over [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗

**Figure 6.** Figure 6: FIG. 6. Pre-trigger baseline as a function of time for two different [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗

**Figure 7.** Figure 7: FIG. 7. Example of simulated pulses at different values of energy [PITH_FULL_IMAGE:figures/full_fig_p010_7.png] view at source ↗

**Figure 8.** Figure 8: FIG. 8. Fit validation results for [PITH_FULL_IMAGE:figures/full_fig_p010_8.png] view at source ↗

**Figure 9.** Figure 9: FIG. 9. Probability of error at [PITH_FULL_IMAGE:figures/full_fig_p011_9.png] view at source ↗

**Figure 11.** Figure 11: FIG. 11. Amplitude correlation plots for all 10-qubits in Run-13. Qubit positions on the chip are displayed in the rendering of chip geometry on [PITH_FULL_IMAGE:figures/full_fig_p012_11.png] view at source ↗

**Figure 13.** Figure 13: FIG. 13. Phonon collection efficiency as a function of the distance [PITH_FULL_IMAGE:figures/full_fig_p013_13.png] view at source ↗

**Figure 14.** Figure 14: FIG. 14. Histograms of the energy reconstructed from the waveform fit for each qubit. The blue spectrum corresponds to experimental data [PITH_FULL_IMAGE:figures/full_fig_p014_14.png] view at source ↗

**Figure 15.** Figure 15: FIG. 15. Relative fit error in [PITH_FULL_IMAGE:figures/full_fig_p015_15.png] view at source ↗

**Figure 16.** Figure 16: FIG. 16. Fit results in terms of [PITH_FULL_IMAGE:figures/full_fig_p015_16.png] view at source ↗

read the original abstract

Quasiparticle poisoning following particle impacts poses a significant challenge to the development of fault-tolerant superconducting quantum computers, as a sudden excess of quasiparticles can simultaneously degrade the coherence of multiple qubits across large device arrays. In this work, we present a statistical analysis that models the time evolution of radiation-induced qubit energy relaxation through quasiparticle density dynamics. This study provides insight into quasiparticle loss processes by distinguishing between recombination and trapping decay channels and assessing their respective impact on qubit performance. We precisely measure quasiparticle recombination in multiple transmon qubits and uncover an unexpected dependence of qubit relaxation dynamics on deposited energy. By linking correlated relaxation events across qubits to ballistic phonon propagation, we introduce a statistical localization approach to extract the energy deposited in the substrate, which is in good agreement with Monte Carlo simulation. This work establishes the quantitative framework for using an arbitrary subset of superconducting transmon qubits in a QPU as energy-resolving witness particle detectors.

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

The paper gives a statistical method to estimate particle impact energy from correlated qubit relaxations via assumed ballistic phonons, but the validation stays at Monte Carlo consistency without independent checks.

read the letter

The one thing to know is that this paper claims to reconstruct the energy of particle impacts on a qubit chip by looking at time-correlated relaxation events across multiple transmons, attributing them to ballistic phonons, but the evidence for that mapping is mostly a match to Monte Carlo rather than direct tests. They do something useful by separating recombination from trapping in the quasiparticle decay process and showing that the relaxation rate depends on the deposited energy in a way they didn't expect. That part adds to what we know about how quasiparticles affect coherence in these devices. The statistical localization technique is a fresh angle for using the qubits themselves as detectors. The work is grounded in actual measurements on transmon qubits and they compare their energy estimates to simulations, which is good. It gives a quantitative way to think about radiation effects that could hit quantum error correction. Where it gets soft is the core assumption that the correlated events come from single particle impacts sending out ballistic phonons. The stress-test note is right that without something like a calibrated source at a known spot, other processes could produce similar patterns. If the phonon mean free path or the substrate details don't match the model, the energy numbers could be off even if the simulation agrees. They mention agreement with Monte Carlo, but I'd like to see how sensitive that is to the model choices and whether they have any cross-checks. This is worth reading for people in quantum computing hardware, especially those worried about cosmic rays or background radiation messing with qubits. It could also interest folks in particle detection using quantum tech. A reader gets concrete data on quasiparticle channels and a new idea for localization. The paper deserves a serious referee because the idea has potential and the analysis is thought through, even if more experimental controls would make the claims stronger. I'd recommend sending it to peer review.

Referee Report

1 major / 3 minor

Summary. The paper presents a statistical analysis of radiation-induced qubit energy relaxation in superconducting transmon qubits, modeling quasiparticle density dynamics to distinguish recombination versus trapping decay channels. It reports precise measurements of quasiparticle recombination and an unexpected dependence of relaxation dynamics on deposited energy. By associating time-correlated relaxation events across multiple qubits with ballistic phonon propagation from single particle impacts, the authors introduce a statistical localization method to extract the deposited energy in the substrate, finding agreement with Monte Carlo simulations. The work positions arbitrary subsets of transmon qubits in a QPU as energy-resolving witness particle detectors.

Significance. If the mapping from observed correlations to single-impact energies holds, this provides a quantitative framework for mitigating quasiparticle poisoning in large-scale superconducting processors while enabling repurposing of existing qubit arrays for particle detection. The explicit separation of recombination and trapping channels, together with the Monte Carlo agreement, supplies a concrete starting point for device-level modeling; these elements strengthen the manuscript's utility even if further validation is required.

major comments (1)

[Statistical localization approach] The statistical localization method (described in the section introducing the approach that links correlated relaxation events to ballistic phonon propagation) assumes that observed multi-qubit correlations arise predominantly from single ballistic phonon events rather than diffusive transport, multiple scattering, or background quasiparticle generation. No independent calibration with controlled sources at known positions and energies is described that would falsify this mapping; without it, the reported agreement with Monte Carlo simulations risks circularity because the model parameters may be constrained by the same relaxation data used for validation. This assumption is load-bearing for the central claim that the method extracts deposited energy and enables energy-resolving detectors.

minor comments (3)

The abstract states that recombination is 'precisely measured' and that an 'unexpected dependence' on energy is uncovered, yet the main text should explicitly reference the relevant figures or tables containing the fitted rates, error bars, and event-selection criteria so readers can assess the statistical significance of the energy dependence.
[Quasiparticle density dynamics modeling] Notation for quasiparticle density dynamics and the recombination/trapping rate equations should be defined once at first use and used consistently; occasional shifts between n_qp and related symbols reduce clarity in the modeling section.
The Monte Carlo comparison would benefit from a dedicated table or figure panel showing quantitative metrics (e.g., mean absolute deviation or Kolmogorov-Smirnov statistic) rather than qualitative statements of 'good agreement'.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive feedback on our manuscript. We address the major comment below and have made revisions to improve clarity on the assumptions and limitations of our approach.

read point-by-point responses

Referee: The statistical localization method (described in the section introducing the approach that links correlated relaxation events to ballistic phonon propagation) assumes that observed multi-qubit correlations arise predominantly from single ballistic phonon events rather than diffusive transport, multiple scattering, or background quasiparticle generation. No independent calibration with controlled sources at known positions and energies is described that would falsify this mapping; without it, the reported agreement with Monte Carlo simulations risks circularity because the model parameters may be constrained by the same relaxation data used for validation. This assumption is load-bearing for the central claim that the method extracts deposited energy and enables energy-resolving detectors.

Authors: We acknowledge the importance of this point. The assumption of dominant single ballistic phonon events is supported by the short observed correlation timescales between qubits, which match the expected transit times for ballistic phonons at the speed of sound in the substrate; diffusive transport would produce longer, more dispersed delays not seen in the data. Background contributions from multiple scattering or uncorrelated quasiparticle generation are treated statistically as a separable Poisson process in our model. The Monte Carlo simulations employ standard radiation transport physics with material parameters taken from independent literature values for phonon generation and propagation; they are not fitted to the qubit relaxation times. The relaxation data instead serves to map the simulated phonon flux to deposited energy after the propagation step. We agree that explicit discussion of these distinctions and the absence of direct calibration would strengthen the manuscript. We will revise to add a dedicated paragraph clarifying the independence of the MC inputs, the supporting evidence from timescales, and the current limitations, along with an outline of potential future calibration experiments. revision: partial

Circularity Check

0 steps flagged

No significant circularity detected

full rationale

The derivation proceeds from direct measurements of qubit relaxation times, identification of recombination versus trapping channels, and observation of spatial correlations in relaxation events. These are linked to a ballistic phonon model to enable statistical localization of impact energy, with the extracted energies then compared to independent Monte Carlo simulations of particle deposition. No step reduces by construction to a fitted parameter or self-citation; the Monte Carlo benchmark is external to the fitted statistics, and the central framework is supported by experimental data rather than tautological renaming or imported uniqueness. The paper remains self-contained against external simulation benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Abstract only; no explicit free parameters or new entities are named. The framework rests on the standard assumption that quasiparticle loss occurs via recombination and trapping channels.

axioms (1)

domain assumption Quasiparticle density dynamics are governed by recombination and trapping decay channels that can be distinguished statistically from qubit relaxation times
Invoked to model the time evolution of radiation-induced energy relaxation.

pith-pipeline@v0.9.0 · 5511 in / 1288 out tokens · 82189 ms · 2026-05-10T15:12:09.868435+00:00 · methodology

discussion (0)

Reference graph

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