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REVIEW 4 major objections 6 minor 1 cited by

Low-Frequency Noise Performance of Microstrip-Coupled Lumped-Element Aluminum KIDs using Hydrogenated Amorphous Silicon Parallel-Plate Capacitors for NEW-MUSIC

T0 review · 4 major / 6 minor · reviewed 2026-08-03 · deepseek-v4-flash

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Pith's one-line read Kinetic inductance detectors with hydrogenated amorphous silicon capacitors stay photon-noise-limited down to about 0.1 Hz, despite the dielectric's potential two-level-system noise.

desk verdict Useful first low-frequency noise data on a-Si:H PPC KIDs, but the abstract's 'establish' oversells an extrapolated optical-load claim. read the letter →

arxiv 2511.08898 v2 pith:M34LSTZB submitted 2025-11-12 astro-ph.IM

Simon Hempel-Costello , Andrew D. Beyer , Dan Cunnane , Peter K. Day , Fabien Defrance , Cliff Frez , Adriana Gavidia , Sunil R. Golwala
show 6 more authors
Junhan Kim Jean-Marc Martin Yann Sadou Jack Sayers Shibo Shu Shiling Yu
This is my paper · ORCID
classification astro-ph.IM
keywords kineticinductancedetectorstwo-level-systemnoisehydrogenatedamorphoussiliconparallel-platecapacitorslow-frequencygeneration-recombinationsubmillimeterastronomyNEW-MUSIC
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

This paper establishes that a detector architecture—kinetic inductance detectors (KIDs) that use hydrogenated amorphous silicon (a-Si:H) parallel-plate capacitors—does not suffer from the low-frequency two-level-system (TLS) noise that such dielectric layers can introduce. Under dark conditions, the detectors are generation-recombination noise dominated down to 0.1 Hz; under optical load, they are likely dominated by generation-recombination plus photon noise down to tenths of a hertz or lower. This matters because the compact, microstrip-coupled design is needed for a planned six-band submillimeter camera, and the result means the detectors can be read out at the slow modulation rates used in astronomical scanning. The paper also sets upper limits on TLS noise in the a-Si:H material at sub-hertz frequencies that are consistent with extrapolations from higher-frequency measurements.

What carries the argument

Two elements carry the argument. First, a two-tone IQ readout that places an on-resonance probe tone and an off-resonance monitor tone at baseband, which removes correlated multiplicative electronics noise (when the off-resonance tone is commissioned) and avoids additive amplifier 1/f noise, allowing noise PSDs to be measured down to 0.1 Hz. Second, a TLS noise scaling relation, S_TLS = S_r^TLS (T/246mK)^{-0.8} (A/A_r)(E/E_r), which extrapolates prior higher-frequency TLS measurements of a-Si:H PPCs to the test detector's area, temperature, and stored electric field, enabling direct comparison of expected TLS noise with the observed dark and optical-load spectra.

What would settle it

Measure the noise PSD of the same detectors under an 180 K optical load down to 0.01 Hz using the two-tone setup with the off-resonance monitor tone enabled; if the PSD below 0.1 Hz rises above the extrapolated GR+photon level (the blue dashed line in Fig. 4) by more than a factor consistent with the dark low-frequency excess, the photon-noise-limited claim fails.

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Extended reading notes

Core claim

The central claim is that aluminum microstrip-coupled, parallel-plate-capacitor, lumped-element kinetic inductance detectors (Al/a-Si:H MS-PPC-LEKIDs) are generation-recombination noise dominated down to 0.1 Hz under dark conditions and likely dominated by generation-recombination plus photon noise down to tenths of a hertz or lower under optical load. This holds despite the a-Si:H parallel-plate capacitors, a potential source of two-level-system noise. By comparing measured noise power spectral densities to TLS noise scaled from prior 0.1–10 kHz measurements using a power-law extrapolation, the authors obtain upper limits on low-frequency TLS noise (3.5 times the broken power-law model and

Load-bearing premise

The photon-noise-limited conclusion rests on extrapolating the noise level measured above 100 Hz under a 180 K optical load unchanged down to 0.01 Hz, assuming no new low-frequency noise source—TLS or electronics—appears under optical load.

Editorial extensions

If this is right

  • NEW-MUSIC's detectors will be photon-noise-limited under on-sky loads of 40–150 K, supporting slow-scan (0.5 deg/s) observations at angular scales of 1–5 degrees.
  • a-Si:H PPCs are validated as a viable dielectric for KIDs in low-modulation-rate applications, not only in the NEW-MUSIC design.
  • The upper limits on TLS noise (3.5x broken power law, 56x f^−0.5) quantify the worst-case low-frequency noise contribution of the dielectric, bounding detector performance.
  • The two-tone IQ measurement approach can be reused for sub-0.1 Hz noise characterization of other KID or resonator architectures.
  • The crossing point where TLS noise would overtake photon noise is conservatively 0.1–0.2 Hz, leaving a comfortable margin for the 1–5 degree scan requirement.

Reading between the lines

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

  • If the low-frequency rise in the dark PSD is, as the authors suspect, correlated electronics noise rather than TLS, the actual TLS noise could lie far below their upper limits; the photon-noise-limited regime could then extend to 0.01 Hz or lower, a testable prediction once the off-resonance tone is fully commissioned.
  • The two-tone IQ readout's noise-removal scheme is not KID-specific; applying it to other superconducting detector readouts (e.g., transition-edge sensors or microwave SQUID multiplexers) could push their low-frequency noise characterization to millihertz levels.
  • The success with a-Si:H suggests other low-TLS-loss deposited dielectrics (such as silicon nitride or silicon dioxide) might be substituted into PPC-KIDs, provided they pass the same low-frequency noise test.
  • A direct extension would be to measure the same detectors with the off-resonance tone active under dark and 180 K loads down to 0.01 Hz; a flat PSD at the extrapolated GR+photon level would confirm the photon-noise-limited claim without relying on extrapolation.
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Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

4 major / 6 minor

Summary. The paper reports low-frequency noise measurements of Al/a-Si:H microstrip-coupled parallel-plate-capacitor lumped-element kinetic inductance detectors (MS-PPC-LEKIDs) developed for the NEW-MUSIC camera. Under dark conditions, the measured PSDs are claimed to be generation-recombination (GR) noise dominated down to 0.1 Hz. Using scaling relations based on prior TLS measurements of a-Si:H PPCs [7], the authors derive approximate upper limits on TLS noise (3.5x the broken power-law model and 56x the f^-0.5 extrapolation) from the dark PSDs. Under optical load (T=180 K), the GR+photon noise measured above 100 Hz in earlier work is extrapolated to low frequency and compared with scaled TLS-noise curves; the authors conservatively conclude that photon noise will dominate down to tenths of a Hz and possibly lower. The abstract states that these results 'establish' that the design will be photon-noise-limited under observing conditions.

Significance. If the conclusions hold, this work provides an important validation of a-Si:H parallel-plate capacitors as a viable low-TLS-noise technology for KIDs in astronomy, where low-frequency stability is required. The paper's strengths include the use of an independent TLS prediction from prior published measurements (no free parameter is tuned to force agreement), conservative upper limits derived from dark data, and a two-tone readout system designed to address correlated electronics noise even though the monitor tone was not fully commissioned. The results are useful for the NEW-MUSIC detector development and for the broader KID community considering a-Si:H PPCs. However, the central quantitative claim rests on an extrapolation rather than a direct low-frequency optical-load measurement, and the manuscript itself contains a contradiction in the TLS scaling description that needs resolution.

major comments (4)
  1. [Abstract; Sec. IV, Fig. 4] The abstract states that the results 'establish that our MS-PPC-LEKID design for NEW-MUSIC will be photon-noise-limited,' but the body text uses 'likely' and 'conservatively concluded.' Under optical load, noise is only reliably measured above 100 Hz (from [1], without the two-tone setup) and is extrapolated to 0.01 Hz in Fig. 4. This is a projection, not a direct measurement, and any new low-frequency noise source under optical load would invalidate it. The abstract and conclusion should be reworded to match the evidence, e.g., 'consistent with being photon-noise-limited' or 'likely photon-noise-limited.'
  2. [Sec. IV, Fig. 3 caption] The TLS upper limits are described as 'approximate fits' and 'approximate upper limits' of 3.5x and 56x, but no fitting procedure, confidence level, or uncertainty on the PSD estimates is provided. These factors are load-bearing for the conclusion that TLS will not dominate at low frequency. Please give a reproducible fitting method and state statistical uncertainties or explicitly label these as order-of-magnitude estimates.
  3. [Sec. III, Eq. (1); Sec. IV, Fig. 4 caption] There is a contradiction in the TLS scaling. Eq. (1) gives S_TLS ∝ E/E_r, so if the stored power (and hence the electric field E) decreases under optical load, S_TLS should decrease. However, the Fig. 4 caption states that the scaled TLS model curves 'increase because the stored power decreases.' This inconsistency affects the quantitative comparison and the conclusion. Please correct either the equation or the text and justify the scaling direction.
  4. [Sec. II, footnote 1; Sec. IV] The off-resonance monitor tone intended to remove correlated multiplicative electronics noise was not commissioned. The authors note that the low-frequency rise in dark data may be correlated electronics rather than TLS. This makes the TLS upper limits conservative, but it also means there is no direct low-frequency measurement under optical load. The manuscript should present the photon-noise-limited conclusion as a testable prediction, not an established result, and should emphasize this limitation in the abstract or conclusion.
minor comments (6)
  1. [Sec. I, Introduction] Typo: 'provide access to a a wide range' should be 'to a wide range.'
  2. [Sec. IV, Optical load paragraph] Typo: 'dependence of responsibility and photon noise' should likely be 'dependence of responsivity and photon noise.'
  3. [Sec. IV, last paragraph] Duplicate word: 'If the prediction from from [7]' should be 'from [7].'
  4. [Abstract] The acronym expansion 'MUltiband' is unconventional; please use 'Multiband' or provide the official expansion.
  5. [Fig. 3 caption] The color names 'mustard' and 'yellow-green' are difficult to identify; use standard color names or line styles in the caption and text.
  6. [Sec. III, Eq. (1)] The parameters a, b, c, d of the broken power law in Eq. (2) are not defined here; please provide the values or refer explicitly to [7] with a short summary, since the scaling and extrapolation rely on them.

Circularity Check

0 steps flagged · score 0.0 of 10

No constructional circularity; the TLS and GR+photon inputs are prior independent measurements, and the new dark data provide only conservative upper limits.

full rationale

The paper's derivation chain is not circular. The low-frequency TLS expectation is imported from prior published measurements [7] via Eq. (1) and Eq. (2); these are not fitted to the current dark/optical PSDs. The dark-data analysis produces only upper limits on TLS noise ('we can set upper limits by fitting the f≤100 Hz form to the observed data'), and these limits are deliberately conservative: the paper notes 'We have no definite evidence it is TLS... the rise is correlated electronics noise.' No fitted parameter is renamed as a prediction; the 'prediction' is [7]'s scaling, and the new data could in principle have exceeded it. The optical-load conclusion extrapolates the >100 Hz GR+photon measurement reported in [1] and the [7] TLS scaling down to 0.01 Hz; this is an extrapolation/evidence limitation, not a circular reduction. The off-resonance monitor tone was not commissioned (footnote 1), weakening the low-frequency limits, but that is a correctness risk rather than a circularity. Self-citations [1] and [7] are load-bearing for context, but they are independent, externally falsifiable measurements on a different resonator/architecture, so they do not constitute circular support.

Assumptions & free parameters 5 free parameters · 4 assumptions · 0 invented entities

The central claim rests on scaling laws and noise models inherited from prior work by the same group; the new data constrains only the product of those assumptions.

free parameters (5)
  • TLS temperature scaling exponent α = -0.8 (Eq. 1)
    Adopted from prior work [7]; fitted to TLS noise data at 0.1-10 kHz; used to scale the low-frequency TLS prediction.
  • Broken power-law TLS spectrum parameters (a,b,c,d) = Not given numerically; slopes f^-1 and f^-0.5
    Adopted from fits in [7] (Eq. 2); used to extrapolate TLS noise below 100 Hz.
  • Reference TLS noise level S^r_TLS = Reference at T=246 mK, area A_r, field E_r (from [7])
    Defines the normalization for Eq. 1; measured in prior work.
  • Dark-PSD upper-limit scale factors = 3.5 (broken power-law model) and 56 (f^-1 extrapolation)
    Derived from approximate fits of the TLS models to the measured dark PSD; used as TLS noise upper limits.
  • Optical-load GR+photon noise PSD level = From 180 K load, measured in [1]
    Extrapolated to low frequency (Fig. 4); central to the photon-noise-limited claim.
assumptions (4)
  • domain assumption TLS noise scales as S_TLS ∝ T^-0.8 * A * E (Eq. 1) across frequency, temperature, and geometry
    Assumed from [7] and used to predict low-frequency TLS noise in the new devices (Sec. III).
  • domain assumption TLS noise spectrum follows a broken power law with f^-1 below 100 Hz and f^-0.5 above (Eq. 2)
    Adopted from [7]; used to extrapolate TLS noise to 0.1 Hz and to fit upper limits (Sec. IV).
  • domain assumption No additional noise source appears between 100 Hz and 0.01 Hz under optical load
    Needed for the blue dashed extrapolation in Fig. 4; not directly measured below 100 Hz.
  • domain assumption The low-frequency rise in the dark PSD, if any, can be wholly attributed to TLS for the purpose of setting upper limits
    The authors state this is conservative and that the rise may actually be correlated electronics noise (footnote 1).

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Cite this review

Pith. "Pith review of Low-Frequency Noise Performance of Microstrip-Coupled Lumped-Element Aluminum KIDs using Hydrogenated Amorphous Silicon Parallel-Plate Capacitors for NEW-MUSIC." pith.science (2026). https://pith.science/paper/M34LSTZB

@misc{pith2026251108898,
  author       = {Pith},
  title        = {Pith review of: Low-Frequency Noise Performance of Microstrip-Coupled Lumped-Element Aluminum KIDs using Hydrogenated Amorphous Silicon Parallel-Plate Capacitors for NEW-MUSIC},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/M34LSTZB}},
  note         = {Machine review of arXiv:2511.08898}
}
read the original abstract

We present measurements of the low-frequency noise of microstrip-coupled, lumped-element aluminum kinetic inductance detectors that use hydrogenated amorphous silicon parallel-plate capacitors (Al/a-Si:H MS-PPC-LEKIDs), which are under development for the Next-generation Extended Wavelength Multiband Submillimeter Inductance Camera (NEW-MUSIC). We show that, under dark conditions, these devices are generation recombination (GR) noise dominated down to 0.1 Hz and, under optical load, they are likely dominated by GR and photon noise down to tenths of a Hz and possibly lower, both in spite of the use of a-Si:H PPCs. Our measurements set limits on the low-frequency two-level-system (TLS) noise of the a-Si:H material that are consistent with higher frequency measurements in the 0.1-10 kHz regime. These results establish that our MS-PPC-LEKID design for NEW-MUSIC will be photon-noise-limited under a range of observing conditions and, more generally, that a-Si:H PPC-KIDs are a viable new detector technology for even low modulation-rate applications such as astronomy.

Figures

Figures reproduced from arXiv: 2511.08898 by the authors.

Figure 2
Figure 2. TLS noise performance of a reference Nb superconducting resonator [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 1
Figure 1. Two-tone IQ measurement setup. I and Q signals at tens to hundreds [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 3
Figure 3. Dark noise data and TLS noise models. Blue: Noise PSD under dark [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figures from the paper (1 more)
Figure 4
Figure 4. Figure 4: Noise PSD under optical load, compared to dark noise PSD and [PITH_FULL_IMAGE:figures/full_fig_p003_4.png]

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Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. An Open Source RFSoC-based Readout Electronics System for Arrays of Kinetic Inductance Detectors and Superconducting Resonators

    physics.ins-det 2026-08 conditional novelty 4.0 of 10

    A two-channel RFSoC-based readout system reads up to 2048 kinetic inductance detectors with noise low enough for detector-limited operation on sky.

Reference graph

Works this paper leans on

9 extracted references · 6 canonical work pages · cited by 1 Pith paper

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