REVIEW 2 major objections 4 minor 37 references
Low two-level-system noise in hydrogenated amorphous silicon
T0 review · 2 major / 4 minor · reviewed 2026-08-11 · deepseek-v4-flash
Pith's one-line read Hydrogenated amorphous silicon capacitors show TLS noise comparable to crystalline substrates, beating prior amorphous dielectrics by a factor of 5 or more.
desk verdict New a-Si:H TLS noise result is likely a real advance, but the >5 improvement claim depends on a faulty extrapolation of the a-SiC:H comparison point. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The measurement chain: each device is a 50 Ω coplanar-waveguide feedline inductively coupled to six lumped-element LC resonators, each made of niobium with an inductor and two a-Si:H parallel-plate capacitors in series. Noise time-streams are rotated to the frequency-dissipation basis using a two-tone calibration, and fractional-frequency noise power spectral densities are fit to a model $a\nu^{\alpha} + b$ with $\alpha$ fixed to −0.5. The extracted amplitude $a$ at 1 kHz is the TLS noise level, compared across stored power (photon number) and against literature values by overlaying the measurement envelope on a reproduced figure from a review.
What would settle it
A direct measurement of the fractional-frequency noise power spectral density below 100 Hz on these same a-Si:H resonators would test the fixed-slope assumption: if the noise rises above the extrapolated −0.5 slope line, the reported $S_{\mathrm{TLS}}$ at 1 kHz would still stand but the integrated noise below 100 Hz would be higher than modeled. Alternatively, fabricating the same a-Si:H film into an interdigitated capacitor resonator and comparing $S_{\mathrm{TLS}}$ at fixed photon number would test whether the low noise is intrinsic to the film or an artifact of the parallel-plate geometry.
Extended reading notes
Core claim
The two-level-system (TLS) fractional-frequency noise measured at 1 kHz in niobium lumped-element resonators with a-Si:H parallel-plate capacitors is 8–80 times lower than previous a-Si:H microstrip results, 5–50 times lower than a-SiC:H, more than 100 times lower than silicon nitride, and comparable to resonators on crystalline silicon and sapphire. These results were obtained with two PECVD a-Si:H recipes, and the low noise is consistent with the previously reported low loss tangent of the same films. The authors conclude that a-Si:H PPCs are a viable low-noise alternative to coplanar-waveguide and interdigitated-capacitor architectures for superconducting resonators.
Load-bearing premise
The analysis assumes that between 200 Hz and 2 kHz the measured frequency noise is exactly a TLS component with spectral slope −0.5 plus white noise, so that a single amplitude extracted from each fit represents the TLS level.
Editorial extensions
If this is right
- Parallel-plate-capacitor kinetic inductance detectors can be built with a-Si:H without the previously expected TLS noise penalty, shrinking detector footprint and reducing stray-light sensitivity.
- Multilayer superconducting circuits, including microstrip resonators and qubit architectures, become feasible with a deposited dielectric that approaches crystalline noise levels.
- The factor-of-5-plus improvement over the best prior amorphous dielectrics warrants revisiting applications where amorphous dielectrics were ruled out by TLS noise.
- The result strengthens the connection between low loss tangent and low TLS noise in a-Si:H, supporting the tunneling model's fluctuation-dissipation predictions.
Reading between the lines
- If the a-Si:H TLS noise is set by the film's intrinsic defect density, further reduction might be possible by tuning deposition temperature or hydrogen content, potentially approaching single-crystal limits.
- The fixed-slope fitting assumption ($\alpha = -0.5$) should be tested at audio frequencies below 100 Hz, where recent measurements on other amorphous dielectrics show a transition to a steeper slope.
- A direct side-by-side measurement of the same a-Si:H film in both parallel-plate and interdigitated capacitor geometries on one setup would confirm that the low noise is intrinsic to the film rather than a geometric effect.
- The comparison to literature relies on one dataset extrapolated from 10 Hz to 1 kHz; a direct measurement at 1 kHz on that same material would sharpen the claimed improvement.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This paper reports measurements of two-level-system (TLS) frequency noise in hydrogenated amorphous silicon (a-Si:H) deposited by two PECVD variants and integrated into niobium lumped-element resonators with parallel-plate capacitors. The authors measure fractional-frequency noise PSDs for 18 resonances across five devices at 230 mK, fit a sum of white noise and a TLS term with spectral slope α fixed to −0.5 over 200 Hz to 2 kHz, and extract TLS noise amplitudes at 1 kHz as a function of stored photon number. They cross-check two devices at NIST at 20 mK, finding agreement within about a factor of two, and compare their results to a literature compilation. The central claim is that their a-Si:H resonators improve on the best previous amorphous-dielectric TLS noise by a factor >5 and approach crystalline-dielectric performance.
Significance. If validated, the quantitative claim would establish PPC-based superconducting resonators with a-Si:H as a practical low-noise alternative to CPW and IDC devices, with potential impact on KID design and multi-layer qubit architectures. The paper's strengths include systematic power and temperature sweeps, a cross-laboratory check on the same devices, the use of a well-established readout and calibration procedure, and explicit acknowledgment of limitations such as the 2–3 dBm power calibration uncertainty. The main weakness is an internal inconsistency in the literature comparison, which undermines the abstract's '>5' factor for 'other amorphous dielectrics' as currently presented.
major comments (2)
- [Figure 5 and the paragraph beginning 'In order to compare our a-Si:H TLS noise results...'] The comparison point K (a-SiC:H from Kouwenhoven et al.) is extrapolated from 10 Hz to 1 kHz using α = −1, but the same reference, as described earlier in this paper, reports α ≈ −1 only below 100 Hz and α ≈ −0.5 above 100 Hz to 1 kHz. Using the correct piecewise extrapolation raises the K point by a factor of 100/(10*sqrt(10)) ≈ 3.16, changing the claimed 5–50× improvement over K to roughly 1.6–16×. The abstract's claim of '>5' improvement over other amorphous dielectrics is therefore not established by the presented comparison. The authors should either use the piecewise slope or rephrase the claim to be specific to a-Si:H (point H), which is unaffected by this issue.
- [Figure 3 and the paragraph defining the red envelope] The red envelope in Figure 3 is defined by eye, and three outlier datasets are excluded without a stated quantitative criterion. Since the factor '>5' in the abstract is derived from the lower edge of this envelope in the Figure 5 overlay, the authors should provide a reproducible definition of the envelope (for example, a fixed percentile of the datasets or the range containing a stated fraction of resonator datasets) and report how the lower edge and the comparison factors change if the outliers are included.
minor comments (4)
- [Figure 2 and the fitting procedure] The fixed slope α = −0.5 is motivated by fits at high feedline readout power, but the paper does not quantify the scatter in α across the different resonators or powers used to set this fixed value. A brief sensitivity check of the extracted amplitude a to plausible variations in α would strengthen the robustness of the reported STLS values.
- [Figure 4 and the Caltech–NIST comparison] The 2–3 dBm power calibration uncertainty is invoked to explain the Caltech–NIST discrepancy. Since the photon-number axis in Figures 3–5 depends directly on the feedline power, the authors should state how this uncertainty propagates to N and whether it affects the placement of the red envelope relative to the literature points plotted at nominal powers.
- [Figure 1 and calibration description] The sentence 'The direction − − − →B1B2 corresponds to the frequency direction' uses a malformed arrow that is difficult to read; please typeset the vector notation properly.
- [Results section, the comparison paragraph] The phrase 'We see that the STLS(ν = 1 kHz) results presented in this article are 8 – 80 times lower than previous measurements for a-Si:H (H)' would benefit from specifying whether the range reflects the full spread of the red envelope or a single representative value, given the envelope's finite width.
Circularity Check
No circular derivation: measured TLS noise compared to independent literature; the only self-citations are supporting, not load-bearing.
full rationale
The paper reports a direct measurement rather than a model-derived prediction. The central claim that the a-Si:H PPC resonators achieve TLS noise '>5' times lower than prior amorphous dielectrics is obtained by fitting each measured fractional-frequency PSD to a * nu^alpha + b, plotting the fitted amplitude a at 1 kHz against photon number, and overlaying the resulting envelope on independent literature data from Zmuidzinas' review plus the a-SiC:H, SiNx, and Si3N4 points. Fixing alpha = -0.5 from high-power fits is an empirical constraint on the measurement model, not a parameter fitted to the target quantity and then renamed as a prediction: the reported S_TLS values are the fitted amplitudes themselves, not outputs of a theory that already contains the answer. The only self-citations are to Defrance et al. 2024 for fabrication details, device geometry, and the photon-number conversion formula; these support the apparatus and calibration but do not determine the noise results. The potential issue of extrapolating the a-SiC:H literature point from 10 Hz to 1 kHz using alpha = -1 while the same reference reports a two-slope spectrum is an internal-consistency and accuracy concern about the literature comparison, not circularity: even if the comparison factor is overstated, the authors' measured noise levels are not equal to their inputs by construction. No equation is defined in terms of the claim, no fitted parameter is presented as a prediction, and no load-bearing argument reduces to a self-citation. Score 1 reflects only the minor, non-load-bearing self-citations to the prior loss-tangent paper.
Assumptions & free parameters
free parameters (2)
- TLS spectral slope alpha =
-0.5 (fixed from high-power fits)
- Comparison envelope (red envelope) =
Hand-drawn; excludes three outlier datasets
assumptions (4)
- domain assumption Frequency-noise PSD is modeled as a*nu^alpha + b with alpha = -0.5 over 200 Hz to 2 kHz.
- domain assumption TLS noise scales as T^-beta, P^-0.5, and nu^alpha.
- domain assumption Stored photon number N follows Eq. (1) using fitted Q factors and feedline power.
- domain assumption Measured frequency noise originates in the a-Si:H film TLS, not interface or readout effects.
Cite this review
Pith. "Pith review of Low two-level-system noise in hydrogenated amorphous silicon." pith.science (2026). https://pith.science/paper/IULICXUB
@misc{pith2026241209693,
author = {Pith},
title = {Pith review of: Low two-level-system noise in hydrogenated amorphous silicon},
year = {2026},
howpublished = {\url{https://pith.science/paper/IULICXUB}},
note = {Machine review of arXiv:2412.09693}
}
read the original abstract
At sub-Kelvin temperatures, two-level systems (TLS) present in amorphous dielectrics source a permittivity noise, degrading the performance of a wide range of devices using superconductive resonators such as qubits or kinetic inductance detectors. We report here on measurements of TLS noise in hydrogenated amorphous silicon (a-Si:H) films deposited by plasma-enhanced chemical vapor deposition (PECVD) in superconductive lumped-element resonators using parallel-plate capacitors (PPCs). The TLS noise results presented in this article for two recipes of a-Si:H improve on the best achieved in the literature by a factor >5 for a-Si:H and other amorphous dielectrics and are comparable to those observed for resonators deposited on crystalline dielectrics.
Figures
Reference graph
Works this paper leans on
-
[1]
author author J. Gao , author J. Zmuidzinas , author B. A. \ Mazin , author H. G. \ LeDuc ,\ and\ author P. K. \ Day ,\ title title Noise properties of superconducting coplanar waveguide microwave resonators , \ https://doi.org/10.1063/1.2711770 journal journal Applied Physics Letters \ volume 90 ,\ pages 102507 ( year 2007 ) ,\ https://arxiv.org/abs/http...
-
[2]
author author J. Gao , author M. Daal , author J. M. \ Martinis , author A. Vayonakis , author J. Zmuidzinas , author B. Sadoulet , author B. A. \ Mazin , author P. K. \ Day ,\ and\ author H. G. \ Leduc ,\ title title A semiempirical model for two-level system noise in superconducting microresonators , \ https://doi.org/10.1063/1.2937855 journal journal A...
-
[3]
author author J. Gao , author M. Daal , author A. Vayonakis , author S. Kumar , author J. Zmuidzinas , author B. Sadoulet , author B. A. \ Mazin , author P. K. \ Day ,\ and\ author H. G. \ Leduc ,\ title title Experimental evidence for a surface distribution of two-level systems in superconducting lithographed microwave resonators , \ https://doi.org/10.1...
-
[4]
author author W. A. \ Phillips ,\ title title Two-level states in glasses , \ https://doi.org/10.1088/0034-4885/50/12/003 journal journal Reports on Progress in Physics \ volume 50 ,\ pages 1657--1708 ( year 1987 ) NoStop
-
[5]
editor P. Esquinazi ,\ ed.,\ title Tunneling systems in amorphous and crystalline solids , \ \ ( publisher Springer Berlin Heidelberg ,\ address Berlin, Heidelberg ,\ year 1998 ) NoStop
work page 1998
-
[6]
author author C. M\" u ller , author J. H. \ Cole ,\ and\ author J. Lisenfeld ,\ title title Towards understanding two-level-systems in amorphous solids: insights from quantum circuits , \ https://doi.org/10.1088/1361-6633/ab3a7e journal journal Reports on Progress in Physics \ volume 82 ,\ pages 124501 ( year 2019 ) NoStop
-
[7]
author author H. B. \ Callen \ and\ author T. A. \ Welton ,\ title title Irreversibility and Generalized Noise , \ https://doi.org/10.1103/PhysRev.83.34 journal journal Physical Review \ volume 83 ,\ pages 34--40 ( year 1951 ) NoStop
-
[8]
author author O. Noroozian , author J. Gao , author J. Zmuidzinas , author H. G. \ LeDuc ,\ and\ author B. A. \ Mazin ,\ title title Two‐level system noise reduction for microwave kinetic inductance detectors , \ https://doi.org/10.1063/1.3292302 journal journal AIP Conference Proceedings \ volume 1185 ,\ pages 148--151 ( year 2009 ) ,\ https://arxiv.org/...
Show all 37 references
-
[9]
author author J. Zmuidzinas ,\ title title Superconducting microresonators: Physics and applications , \ https://doi.org/10.1146/annurev-conmatphys-020911-125022 journal journal Annual Review of Condensed Matter Physics \ volume 3 ,\ pages 169--214 ( year 2012 ) ,\ https://arx...
-
[10]
author author K. L. \ Denis , author N. T. \ Cao , author D. T. \ Chuss , author J. Eimer , author J. R. \ Hinderks , author W. Hsieh , author S. H. \ Moseley , author T. R. \ Stevenson , author D. J. \ Talley , author K. U.‐yen ,\ and\ author E. J. \ Wollack ,\ title title Fa...
-
[11]
author author A. D. \ Beyer , author M. I. \ Hollister , author J. Sayers , author C. F. \ Frez , author P. K. \ Day ,\ and\ author S. R. \ Golwala ,\ title title Fabricating with crystalline si to improve superconducting detector performance , \ http://stacks.iop.org/1742-659...
2017
-
[12]
author author S. R. \ Golwala , author C. Bockstiegel , author S. Brugger , author N. G. \ Czakon , author P. K. \ Day , author T. P. \ Downes , author R. Duan , author J. Gao , author A. K. \ Gill , author J. Glenn , author M. I. \ Hollister , author H. G. \ LeDuc , author P....
-
[13]
Gao ,\ title The Physics of Superconducting Microwave Resonators ,\ @noop Ph.D
author author J. Gao ,\ title The Physics of Superconducting Microwave Resonators ,\ @noop Ph.D. thesis ,\ school California Institute of Technology ( year 2008 ) NoStop
2008
-
[14]
Kouwenhoven , author G
author author K. Kouwenhoven , author G. van Doorn , author B. Buijtendorp , author S. de Rooij , author D. Lamers , author D. Thoen , author V. Murugesan , author J. Baselmans ,\ and\ author P. de Visser ,\ title title Geometry dependence of two-level-system noise and loss in...
-
[15]
Sun , author S
author author J. Sun , author S. Shu , author Y. Chai , author L. Zhu , author L. Zhang , author Y. Li , author Z. Liu , author Z. Li , author Y. Xu , author D. Yan , author W. Guo , author Y. Wang ,\ and\ author C. Liu ,\ https://arxiv.org/abs/2409.09301 title Cryogenic micro...
2024 arXiv
-
[16]
author author J. M. \ Martinis , author K. B. \ Cooper , author R. McDermott , author M. Steffen , author M. Ansmann , author K. D. \ Osborn , author K. Cicak , author S. Oh , author D. P. \ Pappas , author R. W. \ Simmonds ,\ and\ author C. C. \ Yu ,\ title title Decoherence ...
-
[17]
author author A. D. \ O’Connell , author M. Ansmann , author R. C. \ Bialczak , author M. Hofheinz , author N. Katz , author E. Lucero , author C. McKenney , author M. Neeley , author H. Wang , author E. M. \ Weig , author A. N. \ Cleland ,\ and\ author J. M. \ Martinis ,\ tit...
-
[18]
author author B. A. \ Mazin , author D. Sank , author S. McHugh , author E. A. \ Lucero , author A. Merrill , author J. Gao , author D. Pappas , author D. Moore ,\ and\ author J. Zmuidzinas ,\ title title Thin film dielectric microstrip kinetic inductance detectors , \ https:/...
-
[19]
Bruno , author S
author author A. Bruno , author S. T. \ Skacel , author C. Kaiser , author S. W \"u nsch , author M. Siegel , author A. V. \ Ustinov ,\ and\ author M. P. \ Lisitskiy ,\ title title Investigation of Dielectric Losses in Hydrogenated Amorphoussilicon (a-Si:H) thin Films Using Su...
-
[20]
author author B. T. \ Buijtendorp , author J. Bueno , author D. J. \ Thoen , author V. Murugesan , author P. M. \ Sberna , author J. J. A. \ Baselmans , author S. Vollebregt ,\ and\ author A. Endo ,\ title title Characterization of low-loss hydrogenated amorphous silicon films ...
-
[21]
H \"a hnle , author K
author author S. H \"a hnle , author K. Kouwenhoven , author B. T. \ Buijtendorp , author A. Endo , author K. Karatsu , author D. J. \ Thoen , author V. Murugesan ,\ and\ author J. J. A. \ Baselmans ,\ title title Superconducting Microstrip Losses at Microwave and Submillimete...
-
[22]
author author B. T. \ Buijtendorp , author S. Vollebregt , author K. Karatsu , author D. J. \ Thoen , author V. Murugesan , author K. Kouwenhoven , author S. H\"ahnle , author J. J. A. \ Baselmans ,\ and\ author A. Endo ,\ title title Hydrogenated amorphous silicon carbide: A ...
-
[23]
Defrance , author A
author author F. Defrance , author A. D. \ Beyer , author S. Shu , author J. Sayers ,\ and\ author S. R. \ Golwala ,\ title title Characterization of the low electric field and zero-temperature two-level-system loss in hydrogenated amorphous silicon , \ https://doi.org/10.1103...
-
[24]
author author S. J. \ Weber , author K. W. \ Murch , author D. H. \ Slichter , author R. Vijay ,\ and\ author I. Siddiqi ,\ title title Single crystal silicon capacitors with low microwave loss in the single photon regime , \ https://doi.org/10.1063/1.3583449 journal journal A...
-
[25]
Minutolo , author B
author author L. Minutolo , author B. Steinbach , author A. Wandui ,\ and\ author R. O'Brient ,\ title title A flexible gpu-accelerated radio-frequency readout for superconducting detectors , \ https://doi.org/10.1109/TASC.2019.2912027 journal journal IEEE Transactions on Appl...
-
[26]
note Https://www.ettus.com/ NoStop
-
[27]
author author F. W. \ Carter , author T. S. \ Khaire , author V. Novosad ,\ and\ author C. L. \ Chang ,\ title title scraps: An open-source python-based analysis package for analyzing and plotting superconducting resonator data , \ https://doi.org/10.1109/TASC.2016.2625767 jou...
-
[28]
author author M. S. \ Khalil , author M. J. A. \ Stoutimore , author F. C. \ Wellstood ,\ and\ author K. D. \ Osborn ,\ title title An analysis method for asymmetric resonator transmission applied to superconducting devices , \ https://doi.org/10.1063/1.3692073 journal journal...
-
[29]
Burnett , author T
author author J. Burnett , author T. Lindstr\"om , author M. Oxborrow , author Y. Harada , author Y. Sekine , author P. Meeson ,\ and\ author A. Y. \ Tzalenchuk ,\ title title Slow noise processes in superconducting resonators , \ https://doi.org/10.1103/PhysRevB.87.140501 jou...
-
[30]
Burnett , author L
author author J. Burnett , author L. Faoro , author I. Wisby , author V. L. \ Gurtovoi , author A. V. \ Chernykh , author G. M. \ Mikhailov , author V. A. \ Tulin , author R. Shaikhaidarov , author V. Antonov , author P. J. \ Meeson , author A. Y. \ Tzalenchuk ,\ and\ author T...
-
[31]
Barends ,\ title Photon-detecting superconducting resonators ,\ @noop Ph.D
author author R. Barends ,\ title Photon-detecting superconducting resonators ,\ @noop Ph.D. thesis ,\ school Technische Universiteit Delft ( year 2009 ) NoStop
2009
-
[32]
Kumar , author J
author author S. Kumar , author J. Gao , author J. Zmuidzinas , author B. A. \ Mazin , author H. G. \ LeDuc ,\ and\ author P. K. \ Day ,\ title title Temperature dependence of the frequency and noise of superconducting coplanar waveguide resonators , \ https://doi.org/10.1063/...
-
[33]
author author A. N. \ Ramanayaka , author B. Sarabi ,\ and\ author K. D. \ Osborn ,\ https://arxiv.org/abs/1507.06043 title Evidence for universal relationship between the measured 1/f permittivity noise and loss tangent created by tunneling atoms , \ ( year 2015 ),\ https://a...
2015 arXiv
-
[34]
author author H. G. \ Leduc , author B. Bumble , author P. K. \ Day , author B. H. \ Eom , author J. Gao , author S. Golwala , author B. A. \ Mazin , author S. McHugh , author A. Merrill , author D. C. \ Moore , author O. Noroozian , author A. D. \ Turner ,\ and\ author J. Zmu...
-
[35]
Barends , author N
author author R. Barends , author N. Vercruyssen , author A. Endo , author P. J. \ de Visser , author T. Zijlstra , author T. M. \ Klapwijk ,\ and\ author J. J. A. \ Baselmans ,\ title title Reduced frequency noise in superconducting resonators , \ https://doi.org/10.1063/1.34...
-
[36]
author author S. R. \ Golwala , author A. D. \ Beyer , author D. Cunnane , author P. K. \ Day , author F. Defrance , author C. F. \ Frez , author X. Huang , author J. Kim , author J.-M. \ Martin , author J. Sayers , author S. Shu ,\ and\ author S. Yu ,\ title title NEW-MUSIC: ...
-
[37]
Kov \'a cs , author P
author author A. Kov \'a cs , author P. S. \ Barry , author C. M. \ Bradford , author G. Chattopadhyay , author P. Day , author S. Doyle , author S. Hailey-Dunsheath , author M. Hollister , author C. McKenney , author H. G. \ LeDuc , author N. Llombart , author D. P. \ Marrone...
Reviewed August 11, 2026 · model on record in the stance chip above.
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