Pith. sign in

REVIEW 3 major objections 4 minor 34 references

Propagation velocity measurements of substrate phonon bursts using MKIDs for superconducting circuits

T0 review · 3 major / 4 minor · reviewed 2026-08-10 · deepseek-v4-flash

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗ Review JSON

Pith's one-line read A linear array of MKIDs times phonon bursts in a silicon chip and extracts a longitudinal phonon velocity of 12.9 ± 2.6 mm/µs.

desk verdict Nice qualitative result and a plausible threshold model, but the quantitative fit has a factor-2 algebra error and a 42% velocity mismatch that undermine the extracted vph and η. read the letter →

arxiv 2501.03011 v1 pith:2CPZLNRH submitted 2025-01-06 cond-mat.supr-con

Guy Moshel , Omer Rabinowitz , Eliya Blumenthal , Shay Hacohen-Gourgy This is my paper · ORCID
classification cond-mat.supr-con
keywords kineticinductancedetectorsNISjunctionphononpropagationvelocitysuperconductingcircuitsquasiparticleburstssiliconsubstrateburstdetectionthreshold
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

The paper sets out to measure how fast a localized high-energy phonon burst spreads across a silicon chip that hosts superconducting circuits, and to explain why the apparent speed depends on the burst strength. It injects controllable bursts with a normal metal–insulator–superconductor (NIS) junction and times their arrival at aluminum kinetic-inductance detectors (MKIDs) placed at increasing distances. The central finding is that the apparent velocity rises with NIS drive power, and that a two-term model—ballistic flight at $v_{\mathrm{ph}}$ plus a threshold-limited quasiparticle accumulation time—fits all the data simultaneously. The fit gives the longitudinal phonon velocity in silicon, $v_{\mathrm{ph}} = 12.9 \pm 2.6$ mm/µs, and a phonon-to-quasiparticle conversion efficiency $\eta = 1.3\%$ in the aluminum detectors. If correct, this gives quantum-circuit engineers a direct way to predict how far and how fast radiation-induced errors will propagate across a chip.

What carries the argument

The load-bearing object is the two-term detection-time formula (Eq. 6), which writes the measured time as $t_d = x/v_{\mathrm{ph}} + t_{\mathrm{qp}}$, where $t_{\mathrm{qp}} = N_0^{\mathrm{qp}}/(\eta W_{\mathrm{ph}})$ is the time for the MKID to accumulate the minimum detectable number of quasiparticles. The phonon flux $W_{\mathrm{ph}}$ is modeled from a point source with a flat spectrum and full power conversion, giving $W_{\mathrm{ph}} \propto (L/x)(V_{\mathrm{NIS}}/R_N)$, so $t_{\mathrm{qp}} \propto (x/V_{\mathrm{NIS}})$. This makes the apparent velocity a parallel combination of the true phonon velocity and a power-dependent parasitic velocity, which is the mechanism that explains the observed slowdown at low power.

What would settle it

Direct time-of-flight measurement of longitudinal phonons on the same chip at base temperature, with a calibrated detector threshold, would settle whether the high-power intercept is the true 12.9 mm/µs; if an independent acoustic measurement returns about 9.1 mm/µs, the model's assumptions are biased.

Watch

Extended reading notes

Core claim

The paper's claim is that the apparent propagation velocity of a phonon burst measured by MKIDs is not a material constant: it increases with the injected phonon flux, because each MKID only registers the burst once its quasiparticle population crosses a fixed detection threshold $N_0^{\mathrm{qp}}$. Since the phonon flux reaching a detector falls as $1/x$ with distance, the threshold adds a delay proportional to $x/V_{\mathrm{NIS}}$ on top of the ballistic time $x/v_{\mathrm{ph}}$. Fitting $t_d = x/v_{\mathrm{ph}} + (2\pi/L)(N_0^{\mathrm{qp}} e R_N / \eta)(x/V_{\mathrm{NIS}})$ simultaneously to all detectors and powers yields $v_{\mathrm{ph}} = 12.9 \pm 2.6$ mm/µs and $\eta = 1.3\%$.

Load-bearing premise

The model assumes a point-like ballistic source with a flat phonon spectrum and a detector threshold that does not depend on distance or power; if phonon reflections, local hot spots, or a power-dependent threshold contribute, the fitted velocity is biased.

Editorial extensions

If this is right

  • At high burst energies the apparent velocity approaches the true phonon velocity, so large cosmic-ray-like events should appear to travel at about $12.9$ mm/µs, not at the lower speeds inferred from weak events.
  • The measured efficiency $\eta = 1.3\%$ quantifies how many substrate phonons become quasiparticles in an aluminum MKID, giving a number that microscopic models of the phonon–quasiparticle coupling must reproduce.
  • The same model can convert a measured detection time and distance into an estimate of the burst energy, since the $x/V_{\mathrm{NIS}}$ term ties arrival times to source strength.
  • For a known error threshold in a qubit or readout element, the model predicts the time a burst at distance $x$ takes to cause an error, which sets the spatial range of a single radiation event on a chip.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If the threshold $N_0^{\mathrm{qp}}$ can be tuned, for example by changing readout power, the model predicts that apparent-velocity versus power curves should shift in a specific way; testing this would separate threshold effects from genuine phonon physics.
  • The repeatable, non-statistical deviations from the fit could be used as a diagnostic: mapping them across the chip may reveal localized hotspots or edge reflections, effectively turning the MKID array into a phonon-imaging tool.
  • The same NIS-plus-MKID method could be applied to other substrate materials and to chips with qubits to measure burst velocities in the exact devices where radiation errors matter, rather than in a dedicated test structure.
Share X Bluesky LinkedIn Reddit HN

Signed reviews

No signed human review yet.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 4 minor

Summary. The paper reports a controlled measurement of high-energy phonon bursts in a silicon substrate using a normal metal-insulator-superconductor (NIS) junction as a repeatable phonon source and a linear array of microwave kinetic inductance detectors (MKIDs) as time-resolved phonon sensors. The authors observe that the apparent burst propagation velocity increases with NIS drive power, and they explain this through a model in which the measured detection time is the sum of a ballistic propagation time x/v_ph and an additional threshold-limited quasiparticle accumulation time t_qp = N0_qp/(eta W_ph). Fitting Eq. (6), t_d = x/v_ph + (2*pi/L)(N0_qp e R_N/eta)(x/V_NIS), to all data simultaneously yields v_ph = 12.9 +/- 2.6 mm/micro-s and a phonon-to-quasiparticle conversion efficiency eta = 1.3%. The paper concludes that the model can explain low apparent velocities and can be used to estimate burst-induced error propagation in superconducting circuits.

Significance. If the quantitative claims were established, this would be a valuable contribution to the current discussion of radiation-induced bursts in superconducting quantum circuits: it provides a repeatable, high-time-resolution injection-and-detection scheme, and it identifies a threshold effect that naturally explains power-dependent apparent velocities. A notable strength is that the minimum detectable quasiparticle number N0_qp is calibrated independently from temperature-dependent resonance-frequency shifts (Fig. 5 and Eq. (7)), rather than being treated as a purely free fit parameter. However, the central quantitative results are not yet established: the reported v_ph is 42% above the accepted longitudinal [100] sound velocity in silicon, the model relies on several explicitly acknowledged and untested simplifying assumptions, and Eq. (6) contains a factor-of-two algebra error that changes the extracted eta by a factor of two. The qualitative observation and the proposed mechanism are plausible and interesting, but the paper currently overstates the reliability of the fitted v_ph and eta.

major comments (3)
  1. [Eqs. (5)-(6)] Equation (6) does not follow from Eq. (5). Substituting W_ph(x) = (L/(2*pi*x))(2 V_NIS/(e R_N))(1 - 2*Delta/(e V_NIS)) into t_qp = N0_qp/(eta W_ph) and using 2*Delta << e V_NIS gives t_d = x/v_ph + (pi/L)(N0_qp e R_N/eta)(x/V_NIS), with a prefactor pi/L rather than the printed 2*pi/L. The factor of two changes the derived conversion efficiency from eta = 1.3% to approximately 0.65%, so the reported efficiency is not supported by the algebra as written.
  2. [Fig. 4 and fitted v_ph] The extracted v_ph = 12.9 +/- 2.6 mm/micro-s is obtained by extrapolating t_d/x to 1/V_NIS -> 0, i.e., to infinite NIS drive power. If the threshold-limited quasiparticle term is still non-negligible at the highest measured powers, the intercept is controlled by the assumed 1/V_NIS scaling rather than by a directly observed propagation time. This concern is sharpened by the paper's own statement that the fit shows repeatable deviations possibly originating from hot spots or phonon reflections, effects that are distance- and power-dependent and would bias the intercept. Because the fitted value is 42% above the accepted longitudinal [100] sound velocity in silicon (about 9.1 mm/micro-s), I ask for a direct validation: a plot of t_d/x versus 1/V_NIS showing the extrapolation, a time-of-flight estimate at the highest available power, or a fit that allows power-dependent threshold dynamics. Without such a check, v_ph should be presented as a model-dependent extrapolation rather than as a measured propagation velocity.
  3. [Eqs. (3)-(5) and model assumptions] The derivation of the quantitative fit rests on several assumptions that the manuscript itself acknowledges as rough: a flat phonon emission spectrum, complete conversion of absorbed NIS electrical power into phonons, no phonon attenuation or reflections, a point-like source, and a fixed minimum detectable quasiparticle number N0_qp independent of distance and power. These assumptions are not validated against independent data, and the quoted uncertainty of +/- 2.6 mm/micro-s reflects only statistical fit errors, not systematic errors from these modeling choices. The text should either propagate these systematics into the reported v_ph and eta or explicitly flag both quantities as effective model parameters rather than material parameters.
minor comments (4)
  1. [Conclusion] The word 'cryogenicaly' in the concluding paragraph should be 'cryogenically'.
  2. [Fig. 3 caption] The caption refers to 'D06' while Table I and the text use 'D6'; please harmonize the detector naming throughout.
  3. [Eqs. (3)-(4)] Please state explicitly the units and normalization of the phonon spectral density w_NIS_ph(epsilon) and clarify whether the angle theta in Eq. (3) is a planar angle in the substrate plane or a solid angle; the approximation theta approximately L/x then becomes easier to assess.
  4. [Fig. 4] The paper mentions repeatable deviations but does not show repeated runs or error bars in Fig. 4; adding per-point uncertainties or a representative repeat measurement would help the reader judge the statistical weight of the fit.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: vph and η are fit parameters honestly extracted from data, N0_qp is independently calibrated, and no load-bearing self-citations appear.

full rationale

The paper's central quantitative claim is obtained by explicitly fitting a simplified model, td = x/vph + (2π/L)(N0_qp e R_N / η)(x/V_NIS), to all detection-time data simultaneously (Eq. 6 and Fig. 4). This is a parameter extraction, not a prediction derived from the same fitted quantities: vph and η are not inputs to the model construction, and the threshold term is motivated physically by a fixed minimum detectable QP number and 1/x phonon flux decay rather than defined from the measured td values. The independent calibration of N0_qp from temperature-dependent resonance-frequency shifts using Mattis-Bardeen theory is explicitly stated as 'independent of the td measurements.' No self-citations are used as load-bearing support; all cited background results are external literature on MKIDs, superconductivity, and silicon elasticity. The paper openly reports repeatable deviations and unknown origins ('hot-spots' or 'phonon reflections'), which is a limitation and a correctness concern but not a circularity. Similarly, a skeptical reader's worry that vph is obtained by extrapolating 1/V_NIS → 0, or that the factor in Eq. (6) may not follow from Eq. (5), concerns model robustness and arithmetic, not equivalence-by-construction. Therefore no circular step is identified; the appropriate score is 0.

Assumptions & free parameters 5 free parameters · 5 assumptions · 0 invented entities

The central extraction rests on a simplified model with several untested idealizations; the two main extracted parameters (vph, η) are fit parameters, and the fitted vph disagrees with the known silicon sound velocity.

free parameters (5)
  • vph = 12.9 ± 2.6 mm/µs
    Fitted simultaneously to td versus x and VNIS using Eq. 6; the value is 40% higher than the expected [100] longitudinal sound velocity.
  • η = 1.3%
    Derived from the fitted prefactor of the x/VNIS term in Eq. 6 using RN = 10 kΩ, L ≈ 3.8 mm, and N0_qp/V ≈ 2.5 µm^-3.
  • t0 = 0.3 ± 0.12 µs
    Extrapolated drive pulse start time included in the simultaneous fit; shifts all detection times.
  • N0_qp/V = ≈ 2.5 µm^-3
    Minimum detectable QP density estimated from linewidth-scale frequency shift and A = 2.49 µm^-3 kHz^-1; not fit to td data but sets the threshold scale used in η.
  • L (MKID active length) = ≈ 3.8 mm
    Approximated from device geometry; enters the prefactor and therefore the extracted η.
assumptions (5)
  • ad hoc to paper w_NIS_ph(ε) is independent of ε (zeroth order approximation).
    Adopted to make Eq. (5) analytically tractable; no microscopic justification, and it is not tested.
  • ad hoc to paper All electrical power absorbed by the NIS is converted into phonons.
    Assumed to normalize Wph in Eq. (4); calibration of actual injected phonon flux is absent.
  • domain assumption The NIS acts as a perfect open circuit, so VNIS = 2√(Z0 PNIS).
    Used to convert drive power to junction voltage; the authors note this is approximate and list better power estimation as a possible improvement.
  • domain assumption MKID detection time is t_qp = N0_qp/(η Wph) with a fixed threshold N0_qp.
    Assumes QP accumulation time dominates the delay after the phonon arrival and that the threshold is constant; no power dependence is considered.
  • domain assumption Phonon flux reaching each MKID decays as 1/x with θ ≈ L/x and no attenuation or reflections.
    Geometric model used in Eq. (5); the authors later mention reflections and hot spots as possible causes of unexplained deviations.

how reviews work

0 comments
Cite this review

Pith. "Pith review of Propagation velocity measurements of substrate phonon bursts using MKIDs for superconducting circuits." pith.science (2026). https://pith.science/paper/2CPZLNRH

@misc{pith2026250103011,
  author       = {Pith},
  title        = {Pith review of: Propagation velocity measurements of substrate phonon bursts using MKIDs for superconducting circuits},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/2CPZLNRH}},
  note         = {Machine review of arXiv:2501.03011}
}
read the original abstract

High-energy bursts in superconducting quantum circuits from various radiation sources have recently become a practical concern due to induced errors and their propagation in the chip. The speed and distance of these disturbances have practical implications. We used a linear array of multiplexed MKIDs on a single silicon chip to measure the propagation velocity of a localized high-energy burst, introduced by driving a Normal metal- Insulator-Superconductor (NIS) junction. We observed a reduction in the apparent propagation velocity with NIS power, which is due to the combined effect of reduced phonon flux with distance and the existence of a minimum detectable QP density in the MKIDs. A simple theoretical model is fitted to extract the longitudinal phonon velocity in the substrate and the conversion efficiency of phonons to QPs in the superconductor.

Figures

Figures reproduced from arXiv: 2501.03011 by the authors.

Figure 2
Figure 2. FIG. 2. (a) Signal readout circuit schematic. (b) Pulse sequence [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 1
Figure 1. FIG. 1. (a) Image of the PCB and copper box on which the chip [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 3
Figure 3. FIG. 3. Trajectories of the readout signals after a NIS pulse. (a) [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figures from the paper (1 more)
Figure 4
Figure 4. Figure 4: FIG. 4. Burst detection times for di [PITH_FULL_IMAGE:figures/full_fig_p004_4.png]

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

34 extracted references · 23 canonical work pages

  1. [1]

    McEwen, L

    M. McEwen, L. Faoro, K. Arya, A. Dunsworth, T. Huang, S. Kim, B. Burkett, A. Fowler, F. Arute, J. C. Bardin, et al. , Nature Physics 18, 107 (2022)

    work page 2022

  2. [2]

    P. M. Harrington, M. Li, M. Hays, W. Van De Pontseele, D. Mayer, H. D. Pinckney, F. Contipelli, M. Gingras, B. M. Niedzielski, H. Stickler,et al., arXiv preprint arXiv:2402.03208 (2024)

    arXiv 2024

  3. [3]

    Gr ¨unhaupt, N

    L. Gr ¨unhaupt, N. Maleeva, S. T. Skacel, M. Calvo, F. Levy- Bertrand, A. V . Ustinov, H. Rotzinger, A. Monfardini, G. Cate- lani, and I. M. Pop, Physical review letters121, 117001 (2018)

    work page 2018

  4. [4]

    J. M. Martinis, npj Quantum Information 7, 90 (2021)

    2021

  5. [5]

    Bertoldo, M

    E. Bertoldo, M. Mart ´ınez, B. Nedyalkov, and P. Forn-D ´ıaz, arXiv preprint arXiv:2303.04938 (2023)

    arXiv 2023

  6. [6]

    J. L. Orrell and B. Loer, Physical Review Applied 16, 024025 (2021)

    2021

  7. [7]

    Hosseinkhani, R.-P

    A. Hosseinkhani, R.-P. Riwar, R. Schoelkopf, L. Glazman, and G. Catelani, Physical review applied 8, 064028 (2017)

    work page 2017

  8. [8]

    Henriques, F

    F. Henriques, F. Valenti, T. Charpentier, M. Lagoin, C. Gou- riou, M. Mart ´ınez, L. Cardani, M. Vignati, L. Gr ¨unhaupt, D. Gusenkova, et al., Applied physics letters 115 (2019)

    work page 2019

Show all 34 references
  1. [9]

    V . Iaia, J. Ku, A. Ballard, C. Larson, E. Yelton, C. Liu, S. Pa- tel, R. McDermott, and B. Plourde, Nature Communications13, 6425 (2022)

    2022

  2. [10]

    Swenson, A

    L. Swenson, A. Cruciani, A. Benoit, M. Roesch, C. Yung, A. Bideaud, and A. Monfardini, Applied Physics Letters 96, 263511 (2010)

    2010

  3. [11]

    Gordon, C

    R. Gordon, C. E. Murray, C. Kurter, M. Sandberg, S. Hall, K. Balakrishnan, R. Shelby, B. Wacaser, A. Stabile, J. Sleight, et al., Applied Physics Letters 120 (2022)

    2022

  4. [12]

    Yelton, C

    E. Yelton, C. P. Larson, V . Iaia, K. Dodge, G. La Magna, P. G. Baity, I. V . Pechenezhskiy, R. McDermott, N. A. Kurinsky, G. Catelani, and B. L. T. Plourde, Phys. Rev. B 110, 024519 (2024)

    2024

  5. [13]

    Thorbeck, A

    T. Thorbeck, A. Eddins, I. Lauer, D. T. McClure, and M. Car- roll, PRX Quantum 4, 020356 (2023)

    2023

  6. [14]

    Cardani, F

    L. Cardani, F. Valenti, N. Casali, G. Catelani, T. Charpen- tier, M. Clemenza, I. Colantoni, A. Cruciani, G. D’Imperio, L. Gironi, et al., Nature communications 12, 2733 (2021)

    2021

  7. [15]

    Bargerbos, L

    A. Bargerbos, L. J. Splittho ff, M. Pita-Vidal, J. J. Wesdorp, Y . Liu, P. Krogstrup, L. P. Kouwenhoven, C. K. Andersen, and L. Gr¨unhaupt, Physical Review Applied 19, 024014 (2023)

    2023

  8. [16]

    Ullom, in AIP Conference Proceedings, V ol

    J. Ullom, in AIP Conference Proceedings, V ol. 605 (American Institute of Physics, 2002) pp. 135–140

    2002

  9. [17]

    Blonder, m

    G. Blonder, m. M. Tinkham, and T. Klapwijk, Physical Review B 25, 4515 (1982)

    1982

  10. [18]

    Patel, I

    U. Patel, I. V . Pechenezhskiy, B. Plourde, M. Vavilov, and R. McDermott, Physical Review B 96, 220501 (2017)

    2017

  11. [19]

    Zmuidzinas, Annu

    J. Zmuidzinas, Annu. Rev. Condens. Matter Phys. 3, 169 (2012)

    2012

  12. [20]

    P. K. Day, H. G. LeDuc, B. A. Mazin, A. Vayonakis, and J. Zmuidzinas, Nature 425, 817 (2003)

    2003

  13. [21]

    B. A. Mazin, in AIP Conference Proceedings, V ol. 1185 (Amer- ican Institute of Physics, 2009) pp. 135–142

    2009

  14. [22]

    B. A. Mazin, Microwave kinetic inductance detectors (Califor- nia Institute of Technology, 2005)

    2005

  15. [23]

    Gao, The physics of superconducting microwave resonators (California Institute of Technology, 2008)

    J. Gao, The physics of superconducting microwave resonators (California Institute of Technology, 2008)

    2008

  16. [24]

    Probst, F

    S. Probst, F. Song, P. A. Bushev, A. V . Ustinov, and M. Weides, Review of Scientific Instruments 86 (2015)

    2015

  17. [25]

    Huang, B

    S. Huang, B. Lienhard, G. Calusine, A. Veps ¨al¨ainen, J. Braum ¨uller, D. K. Kim, A. J. Melville, B. M. Niedzielski, J. L. Yoder, B. Kannan,et al., PRX Quantum 2, 020306 (2021)

    2021

  18. [26]

    S. B. Kaplan, Journal of Low Temperature Physics 37, 343 (1979)

    1979

  19. [27]

    S. B. Kaplan, C. Chi, D. Langenberg, J.-J. Chang, S. Jafarey, and D. Scalapino, Physical Review B 14, 4854 (1976)

    1976

  20. [28]

    Burnett, High Precision Readout of Superconducting Res- onators, Ph.D

    J. Burnett, High Precision Readout of Superconducting Res- onators, Ph.D. thesis, PhD thesis (2013)

    2013

  21. [29]

    McSkimin, Journal of applied physics 24, 988 (1953)

    H. McSkimin, Journal of applied physics 24, 988 (1953)

    1953

  22. [30]

    Tinkham, Introduction to superconductivity, V ol

    M. Tinkham, Introduction to superconductivity, V ol. 1 (Courier Corporation, 2004)

    2004

  23. [31]

    D. C. Mattis and J. Bardeen, Physical Review 111, 412 (1958)

    1958

  24. [32]

    J. Gao, J. Zmuidzinas, A. Vayonakis, P. Day, B. Mazin, and H. Leduc, Journal of Low Temperature Physics 151, 557 (2008)

    2008

  25. [33]

    Marchegiani, L

    G. Marchegiani, L. Amico, and G. Catelani, PRX Quantum 3, 040338 (2022)

    2022

  26. [34]

    P. B. Fischer and G. Catelani, SciPost Physics 17, 070 (2024)

    2024

Pith tools

Reviewed August 10, 2026 · model on record in the stance chip above.