pith. sign in

arxiv: 2601.06668 · v4 · submitted 2026-01-10 · ❄️ cond-mat.supr-con

Comparison of Two-Level System Microwave Losses in Pure Bulk Microcrystalline Nb2O5 and NbO2 Oxide Samples

Vishal Ganesan , Jiankun Zhang , Drew G. Wild , Alexey Bezryadin This is my paper

Pith reviewed 2026-05-16 15:22 UTC · model grok-4.3

classification ❄️ cond-mat.supr-con
keywords two-level systemsTLS lossesniobium oxidesNb2O5NbO2microwave cavitiessuperconducting qubits
0
0 comments X

The pith

Bulk Nb2O5 powder exhibits two-level system microwave losses matching models while NbO2 shows none.

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

The paper establishes that commercial Nb2O5 microcrystalline powder displays microwave losses with power saturation and temperature dependence characteristic of two-level systems, in agreement with theoretical models. In contrast, similar measurements on NbO2 powder detect no TLS loss signatures. This comparison is made by placing bulk amounts of the powders inside a superconducting 3D microwave cavity. A reader would care because identifying the specific oxide responsible for losses offers a path to improve niobium-based superconducting qubits and cavities by controlling the surface oxide phase.

Core claim

Using a superconducting 3D cavity, measurements on bulk Nb2O5 oxide powder samples reveal losses that follow the power and temperature behavior expected for TLS and agree with existing models, whereas NbO2 bulk powder samples exhibit no detectable TLS loss signatures. This leads to the proposal that TLS losses in practical Nb cavities could be reduced by having high quality microcrystalline NbO2 dominate over Nb2O5.

What carries the argument

Bulk microcrystalline oxide powders placed in a superconducting 3D microwave cavity to directly compare TLS loss characteristics of Nb2O5 and NbO2.

If this is right

  • Niobium resonators could have lower losses if their natural oxide is engineered to favor the NbO2 phase.
  • Materials-based strategies can isolate contributions from specific oxide phases to TLS losses.
  • Reference data is now available for Nb2O5 and NbO2 phases relevant to quantum devices.
  • Reducing TLS in Nb cavities may improve performance of superconducting qubits and microwave cavities.

Where Pith is reading between the lines

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

  • Similar bulk measurements could be applied to other metal oxides to identify low-loss phases for quantum applications.
  • If thin oxide layers on Nb behave like the bulk powders, phase control during fabrication would directly impact device coherence.
  • Future work might test whether annealing or other treatments can convert Nb2O5 to NbO2 on actual resonator surfaces.

Load-bearing premise

Bulk microcrystalline powder samples accurately represent the thin natural oxide layers on niobium in practical resonators and cavities.

What would settle it

Fabricate niobium resonators with controlled surface oxide phases rich in NbO2 versus Nb2O5 and measure their TLS loss contributions to see if they match the bulk powder results.

Figures

Figures reproduced from arXiv: 2601.06668 by Alexey Bezryadin, Drew G. Wild, Jiankun Zhang, Vishal Ganesan.

Figure 1
Figure 1. Figure 1: FIG. 1: Sample Nb25 [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2: Representative complex Lorentzian fit to the transmission coefficient of the cavity with the sample Nb25 [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3: Control measurements of [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4: Power dependence of the inverse of the intrinsic quality factor [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5: Sample Nb25 [PITH_FULL_IMAGE:figures/full_fig_p009_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6: Sample Nb25 [PITH_FULL_IMAGE:figures/full_fig_p011_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: FIG. 7 [PITH_FULL_IMAGE:figures/full_fig_p012_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: FIG. 8: Comparison of observed and calculated XRD patterns for (a) Nb [PITH_FULL_IMAGE:figures/full_fig_p016_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: FIG. 9: Geometry of the simulation for (a) the substrate-loaded cavity and (b) the substrate + the oxide-sample [PITH_FULL_IMAGE:figures/full_fig_p017_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: FIG. 10: Electric field distribution at resonance along the (a) XY, (b) YZ, and (c) XZ planes. Input power to the [PITH_FULL_IMAGE:figures/full_fig_p018_10.png] view at source ↗
read the original abstract

Losses from two-level systems (TLS) associated with amorphous oxides remain one of the primary limitations to the performance of superconducting qubits and microwave cavities. Niobium resonators are widely used in quantum science experiments, yet niobium's natural oxide layer contains various types of oxides whose relative contributions to TLS loss have not been clearly distinguished. Here, we use a superconducting 3D microwave cavity to measure commercial 99.9\% trace metal pure, microcrystalline oxide powders \ch{Nb2O5} and \ch{NbO2} in bulk amounts. Using this approach, we directly compare the loss characteristics of \ch{Nb2O5} and \ch{NbO2}. Our measurements show that the nominal \ch{Nb2O5} bulk oxide powder samples exhibit losses which have the power and temperature behavior expected for TLS. Moreover, the measurements agree with existing theoretical models. Analogous measurements performed on \ch{NbO2} bulk powder samples do not show any detectable TLS loss signatures. Based on our results we propose that the TLS losses might be reduced if a high quality microcrystalline \ch{NbO2} oxide dominates the \ch{Nb2O5} oxide in practical Nb cavities. These results establish a materials based strategy for isolating oxide specific TLS losses and provide a reference measurement for niobium oxide phases relevant to superconducting quantum devices.

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.

Referee Report

3 major / 2 minor

Summary. The manuscript measures microwave losses from commercial 99.9% pure microcrystalline Nb2O5 and NbO2 bulk powders inside a superconducting 3D cavity. It reports that Nb2O5 powders display power- and temperature-dependent losses whose qualitative behavior matches expectations for two-level systems (TLS) and existing theoretical models, while NbO2 powders show no detectable TLS signatures. The authors conclude that TLS losses in practical Nb cavities might be reduced if a high-quality microcrystalline NbO2 phase dominates the natural oxide layer.

Significance. If the bulk-powder results translate to thin natural oxides, the work supplies a concrete materials strategy for isolating oxide-specific TLS contributions and a reference data set for Nb-based quantum devices. The direct experimental comparison of two distinct Nb oxide phases is useful. However, the significance hinges on an untested proxy assumption whose validity is not demonstrated within the manuscript.

major comments (3)
  1. [Abstract and Discussion] Abstract and Discussion section: the central claim of 'qualitative agreement with TLS models' is presented without quantitative fits, extracted TLS parameters, or reported uncertainties on the loss data. This leaves the agreement observational and prevents a rigorous test of the models cited.
  2. [Methods and Experimental Setup] Methods and Experimental Setup: no morphological, structural, or interface characterization (XRD, SEM, XPS, or grain-size distribution) of the commercial microcrystalline powders is provided. Without this, the assumption that bulk 99.9% pure powders accurately represent the few-nm amorphous or strained natural oxides on Nb surfaces remains untested and load-bearing for the proposed cavity strategy.
  3. [Results] Results section: the absence of detectable TLS loss in NbO2 is stated, but no upper-bound estimate on the TLS loss tangent or comparison of cavity Q values with and without the powder is given, making the 'no detectable signature' claim difficult to quantify or reproduce.
minor comments (2)
  1. Notation: chemical formulas are rendered with the mhchem package; ensure every occurrence of Nb2O5 and NbO2 is consistently formatted and that subscripts are not omitted in figure labels.
  2. Figure clarity: power- and temperature-dependence plots should include error bars (or state that they are smaller than symbols) and explicit legends distinguishing the two oxide samples.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for their careful reading and constructive comments on our manuscript. We address each major comment point by point below, indicating where revisions will be made.

read point-by-point responses

  1. Referee: [Abstract and Discussion] Abstract and Discussion section: the central claim of 'qualitative agreement with TLS models' is presented without quantitative fits, extracted TLS parameters, or reported uncertainties on the loss data. This leaves the agreement observational and prevents a rigorous test of the models cited.

    Authors: We agree that quantitative fits would strengthen the manuscript. In the revised version we will add explicit fits to the standard TLS model in the Discussion, reporting extracted parameters (e.g., loss tangent, relaxation rates) together with uncertainties obtained from the data. The abstract will retain its qualitative phrasing while the main text will enable a more rigorous comparison with the cited models. revision: yes

  2. Referee: [Methods and Experimental Setup] Methods and Experimental Setup: no morphological, structural, or interface characterization (XRD, SEM, XPS, or grain-size distribution) of the commercial microcrystalline powders is provided. Without this, the assumption that bulk 99.9% pure powders accurately represent the few-nm amorphous or strained natural oxides on Nb surfaces remains untested and load-bearing for the proposed cavity strategy.

    Authors: The referee is correct that we relied on the commercial specification without additional in-house structural characterization. We will revise the Methods and Discussion sections to state the proxy assumption explicitly, note its untested character for thin-film oxides, and include any supplier-provided purity and particle-size information. Full XRD/SEM/XPS analysis of the specific batches would require new experiments outside the present study. revision: partial

  3. Referee: [Results] Results section: the absence of detectable TLS loss in NbO2 is stated, but no upper-bound estimate on the TLS loss tangent or comparison of cavity Q values with and without the powder is given, making the 'no detectable signature' claim difficult to quantify or reproduce.

    Authors: We will revise the Results section to report a quantitative upper bound on the TLS loss tangent for NbO2, derived from the measurement noise floor and from direct comparisons of cavity Q with and without the NbO2 powder. This will make the non-detection claim precise and reproducible. revision: yes

Circularity Check

0 steps flagged

No circularity: purely experimental comparison to independent external models

full rationale

The paper reports direct cavity measurements of loss in commercial bulk Nb2O5 and NbO2 powders, observing power and temperature dependence that matches the expected TLS signatures from pre-existing literature models. No parameters are fitted to the present data and then re-used as 'predictions,' no self-definitional relations appear, and no load-bearing self-citations or uniqueness theorems are invoked to close the argument. The central claim therefore rests on empirical observation rather than any reduction of outputs to the paper's own inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Relies on standard TLS theory and assumption that bulk samples proxy surface oxides.

axioms (1)
  • domain assumption TLS exhibit characteristic power and temperature dependent losses as per standard models
    Measurements agree with existing theoretical models for TLS.

pith-pipeline@v0.9.0 · 8021 in / 961 out tokens · 70120 ms · 2026-05-16T15:22:18.391576+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

What do these tags mean?
matches
The paper's claim is directly supported by a theorem in the formal canon.
supports
The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends
The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses
The paper appears to rely on the theorem as machinery.
contradicts
The paper's claim conflicts with a theorem or certificate in the canon.
unclear
Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

61 extracted references · 61 canonical work pages

  1. [1]

    Martinis, K

    John M. Martinis, K. B. Cooper, R. McDermott, M. Steffen, M. Ansmann, K. D. Osborn, K. Cicak, S. Oh, D. P. Pappas, R. W. Simmonds, and C. C. Yu. Decoherence in josephson qubits from dielectric loss.Physical Review Letters, 95(21):210503, 2005

    work page 2005

  2. [2]

    Krantz, M

    P. Krantz, M. Kjaergaard, F. Yan, T. P. Orlando, S. Gustavsson, and W. D. Oliver. A quantum engineer’s guide to superconducting qubits.Appl. Phys. Rev., 6:021318, 2019

    work page 2019

  3. [3]

    Crowley, Russell A

    Kevin D. Crowley, Russell A. McLellan, Aveek Dutta, Nana Shumiya, Alexander P. M. Place, Xuan Hoang Le, Youqi Gang, Trisha Madhavan, Matthew P. Bland, Ray Chang, Nishaad Khedkar, Yiming Cady Feng, Esha A. Umbarkar, Xin Gui, Lila V. H. Rodgers, Yichen Jia, Mayer M. Feldman, Stephen A. Lyon, Mingzhao Liu, Robert J. Cava, Andrew A. Houck, and Nathalie P. de ...

    work page 2023

  4. [4]

    Russell, Xinyuan You, David A

    Andr´ e Valli` eres, Megan E. Russell, Xinyuan You, David A. Garcia-Wetten, Dominic P. Goronzy, Mitchell J. Walker, Michael J. Bedzyk, Mark C. Hersam, Alexander Romanenko, Yao Lu, Anna Grassellino, Jens Koch, and Corey Rae H. McRae. Loss tangent fluctuations due to two-level systems in superconducting microwave resonators.Applied Physics Letters, 126(12):...

    work page 2025

  5. [5]

    Towards understanding two-level-systems in amorphous solids: Insights from quantum circuits.Reports on Progress in Physics, 82(12):124501, 2019

    Clemens M¨ uller, Jared H Cole, and J¨ urgen Lisenfeld. Towards understanding two-level-systems in amorphous solids: Insights from quantum circuits.Reports on Progress in Physics, 82(12):124501, 2019

    work page 2019

  6. [6]

    Three-dimensional niobium coaxial cavity with 0.1-second lifetime.Phys

    Takaaki Takenaka, Takayuki Kubo, Imran Mahboob, Kosuke Mizuno, Hitoshi Inoue, Takayuki Saeki, and Shiro Saito. Three-dimensional niobium coaxial cavity with 0.1-second lifetime.Phys. Rev. Appl., pages –, Feb 2026

    work page 2026

  7. [7]

    Romanenko, R

    A. Romanenko, R. Pilipenko, S. Zorzetti, D. Frolov, M. Awida, S. Belomestnykh, S. Posen, and A. Grassellino. Three- dimensional superconducting resonators att <20 mk with photon lifetimes up toτ= 2 s.Phys. Rev. Appl., 13:034032, Mar 2020

    work page 2020

  8. [8]

    Bruno, G

    A. Bruno, G. de Lange, S. Asaad, K. L. van der Enden, N. K. Langford, and L. DiCarlo. Reducing intrinsic loss in superconducting resonators by surface treatment and substrate removal.Applied Physics Letters, 106(18):182601, 2015

    work page 2015

  9. [9]

    de Ory, David Rodriguez, Maria T

    Marina C. de Ory, David Rodriguez, Maria T. Magaz, V´ ıctor Rollano, Daniel Granados, and Alicia Gomez. Low loss hybrid nb/au superconducting resonators for quantum circuit applications, 2024. 14

    work page 2024

  10. [10]

    Kalboussi, B

    Y. Kalboussi, B. Delatte, S. Bira, K. Dembele, X. Li, F. Miserque, N. Brun, M. Walls, J. L. Maurice, D. Dragoe, and et al. Reducing two-level systems dissipations in 3d superconducting niobium resonators by atomic layer deposition and high temperature heat treatment.Applied Physics Letters, 124(13), Mar 2024

    work page 2024

  11. [11]

    C. M. Quintana, A. Megrant, Z. Chen, A. Dunsworth, B. Chiaro, R. Barends, B. Campbell, Yu Chen, I.-C. Hoi, E. Jeffrey, J. Kelly, J. Y. Mutus, P. J. J. O’Malley, C. Neill, P. Roushan, D. Sank, A. Vainsencher, J. Wenner, T. C. White, A. N. Cleland, and John M. Martinis. Characterization and reduction of microfabrication-induced decoherence in superconductin...

    work page 2014

  12. [12]

    Dielectric surface loss in superconducting resonators with flux-trapping holes.Superconductor Science and Technology, 29(10):104006, aug 2016

    B Chiaro, A Megrant, A Dunsworth, Z Chen, R Barends, B Campbell, Y Chen, A Fowler, I C Hoi, E Jeffrey, J Kelly, J Mutus, C Neill, P J J O’Malley, C Quintana, P Roushan, D Sank, A Vainsencher, J Wenner, T C White, and John M Martinis. Dielectric surface loss in superconducting resonators with flux-trapping holes.Superconductor Science and Technology, 29(10...

    work page 2016

  13. [13]

    Halbritter

    J. Halbritter. On the oxidation and on the superconductivity of niobium.Applied Physics A, 43(1):1–28, 1987

    work page 1987

  14. [14]

    Murthy, Paul Masih Das, Stephanie M

    Akshay A. Murthy, Paul Masih Das, Stephanie M. Ribet, Cameron Kopas, Jaeyel Lee, Matthew J. Reagor, Lin Zhou, Matthew J. Kramer, Mark C. Hersam, Mattia Checchin, Anna Grassellino, Roberto dos Reis, Vinayak P. Dravid, and Alexander Romanenko. Developing a chemical and structural understanding of the surface oxide in a niobium supercon- ducting qubit.ACS Na...

    work page 2022

  15. [15]

    Romanenko and D.I

    A. Romanenko and D.I. Schuster. Understanding quality factor degradation in superconducting niobium cavities at low microwave field amplitudes.Physical Review Letters, 119(26), Dec 2017

    work page 2017

  16. [16]

    Theory of rf superconductivity for resonant cavities.Superconductor Science and Technology, 30(3):034004, jan 2017

    Alex Gurevich. Theory of rf superconductivity for resonant cavities.Superconductor Science and Technology, 30(3):034004, jan 2017

    work page 2017

  17. [17]

    Field-dependent nonlinear surface resistance and its optimization by surface nanos- tructuring in superconductors.Phys

    Takayuki Kubo and Alex Gurevich. Field-dependent nonlinear surface resistance and its optimization by surface nanos- tructuring in superconductors.Phys. Rev. B, 100:064522, Aug 2019

    work page 2019

  18. [18]

    Posen, A

    S. Posen, A. Romanenko, A. Grassellino, O.S. Melnychuk, and D.A. Sergatskov. Ultralow surface resistance via vacuum heat treatment of superconducting radio-frequency cavities.Physical Review Applied, 13(1), Jan 2020

    work page 2020

  19. [19]

    Im- proved rf performance of niobium cavities via in-situ vacuum heat treatment technique.Superconductor Science and Technology, 38(4):045006, Mar 2025

    Yegor Tamashevich, Alena Prudnikava, Alexander Matveenko, Axel Neumann, Oliver Kugeler, and Jens Knobloch. Im- proved rf performance of niobium cavities via in-situ vacuum heat treatment technique.Superconductor Science and Technology, 38(4):045006, Mar 2025

    work page 2025

  20. [20]

    Pozar.Microwave engineering

    David M. Pozar.Microwave engineering. Wiley, Hoboken, NJ, 4th ed edition, 2012. OCLC: ocn714728044

    work page 2012

  21. [21]

    Honasoge, Fabian Kronowetter, Yuki Nojiri, Michael Renger, Kirill G

    Qi-Ming Chen, Meike Pfeiffer, Matti Partanen, Florian Fesquet, Kedar E. Honasoge, Fabian Kronowetter, Yuki Nojiri, Michael Renger, Kirill G. Fedorov, Achim Marx, Frank Deppe, and Rudolf Gross. Scattering coefficients of superconducting microwave resonators. i. transfer matrix approach.Phys. Rev. B, 106:214505, Dec 2022

    work page 2022

  22. [22]

    Honasoge, Fabian Kronowetter, Yuki Nojiri, Michael Renger, Kirill G

    Qi-Ming Chen, Matti Partanen, Florian Fesquet, Kedar E. Honasoge, Fabian Kronowetter, Yuki Nojiri, Michael Renger, Kirill G. Fedorov, Achim Marx, Frank Deppe, and Rudolf Gross. Scattering coefficients of superconducting microwave resonators. ii. system-bath approach.Phys. Rev. B, 106:214506, Dec 2022

    work page 2022

  23. [23]

    M. S. Khalil, M. J. A. Stoutimore, F. C. Wellstood, and K. D. Osborn. Loss dependence on geometry and applied power in superconducting coplanar resonators.J. Appl. Phys., 111:054510, 2012

    work page 2012

  24. [24]

    Probst, F

    S. Probst, F. B. Song, P. A. Bushev, A. V. Ustinov, and M. Weides. Efficient and robust analysis of complex scattering data under noise in microwave resonators.Review of Scientific Instruments, 86(2):024706, 02 2015

    work page 2015

  25. [25]

    Effects of nonmagnetic impurities and subgap states on the kinetic inductance, complex conductivity, quality factor, and depairing current density.Phys

    Takayuki Kubo. Effects of nonmagnetic impurities and subgap states on the kinetic inductance, complex conductivity, quality factor, and depairing current density.Phys. Rev. Appl., 17:014018, Jan 2022

    work page 2022

  26. [26]

    Tuning microwave losses in superconducting resonators.Superconductor Science and Technology, 36(6):063002, apr 2023

    Alex Gurevich. Tuning microwave losses in superconducting resonators.Superconductor Science and Technology, 36(6):063002, apr 2023

    work page 2023

  27. [27]

    Posen, M

    S. Posen, M. Checchin, A. C. Crawford, A. Grassellino, M. Martinello, O. S. Melnychuk, A. Romanenko, D. A. Sergatskov, and Y. Trenikhina. Efficient expulsion of magnetic flux in superconducting radiofrequency cavities for high q applications. Journal of Applied Physics, 119(21):213903, 06 2016

    work page 2016

  28. [28]

    Shichun Huang, Takayuki Kubo, and R. L. Geng. Dependence of trapped-flux-induced surface resistance of a large-grain nb superconducting radio-frequency cavity on spatial temperature gradient during cooldown throughT c.Phys. Rev. Accel. Beams, 19:082001, Aug 2016

    work page 2016

  29. [29]

    Lindstr¨ om, J

    T. Lindstr¨ om, J. E. Healey, M. S. Colclough, C. M. Muirhead, and A. Ya. Tzalenchuk. Properties of superconducting planar resonators at millikelvin temperatures.Phys. Rev. B, 80:132501, Oct 2009

    work page 2009

  30. [30]

    PhD thesis, California Institute of Technology, 2008

    Jiansong Gao.The Physics of Superconducting Microwave Resonators. PhD thesis, California Institute of Technology, 2008

    work page 2008

  31. [31]

    Two-level states in glasses.Reports on Progress in Physics, 50(12):1657–1708, Dec 1987

    W A Phillips. Two-level states in glasses.Reports on Progress in Physics, 50(12):1657–1708, Dec 1987

    work page 1987

  32. [32]

    Zollitsch, Sebastian Meier, Michael Fischer, Peter Eder, Edwar Xie, Kirill G

    Jan Goetz, Frank Deppe, Max Haeberlein, Friedrich Wulschner, Christoph W. Zollitsch, Sebastian Meier, Michael Fischer, Peter Eder, Edwar Xie, Kirill G. Fedorov, and et al. Loss mechanisms in superconducting thin film microwave resonators. Journal of Applied Physics, 119(1), Jan 2016

    work page 2016

  33. [33]

    Burnett, L

    J. Burnett, L. Faoro, and T. Lindstr¨ om. Evidence for interacting two-level systems from the 1/f noise of a superconducting resonator.Nature Communications, 5:4119, 2014

    work page 2014

  34. [34]

    Lara Faoro and Lev B. Ioffe. Interacting tunneling model for two-level systems in amorphous materials and its predictions for the low-temperature properties of glasses.Physical Review B, 91(1):014201, 2015

    work page 2015

  35. [35]

    Bafia, A

    D. Bafia, A. Murthy, A. Grassellino, and A. Romanenko. Oxygen vacancies in niobium pentoxide as a source of two-level system losses in superconducting niobium.Phys. Rev. Appl., 22:024035, Aug 2024

    work page 2024

  36. [36]

    DuBois, Manolo C

    Timothy C. DuBois, Manolo C. Per, Salvy P. Russo, and Jared H. Cole. Delocalized oxygen as the origin of two-level defects in josephson junctions.Physical Review Letters, 110(7), Feb 2013. 15

    work page 2013

  37. [37]

    Burnett, J

    J. Burnett, J. Sagar, O.W. Kennedy, P.A. Warburton, and J.C. Fenton. Low-loss superconducting nanowire circuits using a neon focused ion beam.Physical Review Applied, 8(1), Jul 2017

    work page 2017

  38. [38]

    Verjauw, A

    J. Verjauw, A. Potoˇ cnik, M. Mongillo, R. Acharya, F. Mohiyaddin, G. Simion, A. Pacco, Ts. Ivanov, D. Wan, A. Vanleen- hove, and et al. Investigation of microwave loss induced by oxide regrowth in high-q niobium resonators.Physical Review Applied, 16(1), Jul 2021

    work page 2021

  39. [39]

    Kalboussi, I

    Y. Kalboussi, I. Curci, F. Miserque, D. Troadec, N. Brun, M. Walls, G. Jullien, F. Eozenou, M. Baudrier, L. Maurice, Q. Bertrand, P. Sahuquet, and T. Proslier. Crystallinity in niobium oxides: A pathway to mitigate two-level-system defects in niobium three-dimensional resonators for quantum applications.Phys. Rev. Appl., 23:044023, Apr 2025

    work page 2025

  40. [40]

    Nonequilibrium nonlinear response theory of amplitude-dependent dissipative conductivity in disordered superconductors.Phys

    Takayuki Kubo. Nonequilibrium nonlinear response theory of amplitude-dependent dissipative conductivity in disordered superconductors.Phys. Rev. Appl., 24:064061, Dec 2025

    work page 2025

  41. [41]

    Dhakal, B

    P. Dhakal, B. D. Khanal, A. Gurevich, and G. Ciovati. Field, frequency, and temperature dependencies of the surface resistance of nitrogen diffused niobium superconducting radio frequency cavities.Phys. Rev. Accel. Beams, 27:062001, Jun 2024

    work page 2024

  42. [42]

    Pappas, Michael R

    David P. Pappas, Michael R. Vissers, David S. Wisbey, Jeffrey S. Kline, and Jiansong Gao. Two level system loss in superconducting microwave resonators.IEEE Transactions on Applied Superconductivity, 21(3):871–874, 2011

    work page 2011

  43. [43]

    Wisbey, Jiansong Gao, Michael R

    David S. Wisbey, Jiansong Gao, Michael R. Vissers, Fabio C. S. da Silva, Jeffrey S. Kline, Leila Vale, and David P. Pappas. Effect of metal/substrate interfaces on radio-frequency loss in superconducting coplanar waveguides.Journal of Applied Physics, 108(9):093918, 11 2010

    work page 2010

  44. [44]

    Glazman and Gianluigi Catelani

    Leonid I. Glazman and Gianluigi Catelani. Bogoliubov quasiparticles in superconducting qubits.SciPost Phys. Lect. Notes, page 31, 2021

    work page 2021

  45. [45]

    Barends, J

    R. Barends, J. Wenner, M. Lenander, Y. Chen, R. C. Bialczak, J. Kelly, E. Lucero, P. O’Malley, M. Mariantoni, D. Sank, H. Wang, T. C. White, Y. Yin, J. Zhao, A. N. Cleland, John M. Martinis, and J. J. A. Baselmans. Minimizing quasiparticle generation from stray infrared light in superconducting quantum circuits.Applied Physics Letters, 99(11):113507, 09 2011

    work page 2011

  46. [46]

    C. H. Liu, D. C. Harrison, S. Patel, C. D. Wilen, O. Rafferty, A. Shearrow, A. Ballard, V. Iaia, J. Ku, B. L. T. Plourde, and R. McDermott. Quasiparticle poisoning of superconducting qubits from resonant absorption of pair-breaking photons. Phys. Rev. Lett., 132:017001, Jan 2024

    work page 2024

  47. [47]

    Non-equilibrium superconductivity in quantum-sensing superconducting resonators.Super- conductor Science and Technology, 26(1):015004, nov 2012

    D J Goldie and S Withington. Non-equilibrium superconductivity in quantum-sensing superconducting resonators.Super- conductor Science and Technology, 26(1):015004, nov 2012

    work page 2012

  48. [48]

    P. J. de Visser, D. J. Goldie, P. Diener, S. Withington, J. J. A. Baselmans, and T. M. Klapwijk. Evidence of a nonequilibrium distribution of quasiparticles in the microwave response of a superconducting aluminum resonator.Phys. Rev. Lett., 112:047004, Jan 2014

    work page 2014

  49. [49]

    Formation of niobium hydride precipitates in superconducting qubits.Phys

    Zuhawn Sung, Daniel Bafia, Arely Cano, Akshay Murthy, Jaeyel Lee, Matthew J Reagor, Juan Rubio-Zuazo, Anna Grassellino, and Alexander Romanenko. Formation of niobium hydride precipitates in superconducting qubits.Phys. Rev. Mater., 10:016201, Jan 2026

    work page 2026

  50. [50]

    Direct observation of nanometer size hydride precipitations in superconducting niobium.Scientific Reports, 14(1):26916, 2024

    Zuhawn Sung, Arely Cano, Akshay Murthy, Daniel Bafia, Ekaterina Karapetrova, Martina Martinello, Jaeyel Lee, Anna Grassellino, and Alexander Romanenko. Direct observation of nanometer size hydride precipitations in superconducting niobium.Scientific Reports, 14(1):26916, 2024

    work page 2024

  51. [51]

    Romanenko, A

    A. Romanenko, A. Grassellino, F. Barkov, and J. P. Ozelis. Effect of mild baking on superconducting niobium cavities investigated by sequential nanoremoval.Phys. Rev. ST Accel. Beams, 16:012001, Jan 2013

    work page 2013

  52. [52]

    Romanenko, A

    A. Romanenko, A. Grassellino, D. A. Sergatskov, O. Melnychuk, Y. Trenikhina, A. C. Crawford, A. Rowe, C. P. Welsch, T. Khabiboulline, and V. P. Yakovlev. Intrinsic losses in superconducting niobium cavities at millikelvin temperatures.J. Appl. Phys., 115:184903, 2014

    work page 2014

  53. [53]

    Martinello, M

    M. Martinello, M. Checchin, A. Romanenko, A. Grassellino, S. Aderhold, S. K. Chandrasekeran, O. Melnychuk, S. Posen, and D. A. Sergatskov. Field-enhanced superconductivity in high-frequency niobium accelerating cavities.Phys. Rev. Lett., 121:224801, Nov 2018

    work page 2018

  54. [54]

    Wiley, 8 edition, 2004

    Charles Kittel.Introduction to Solid State Physics. Wiley, 8 edition, 2004

    work page 2004

  55. [55]

    Richard J. D. Tilley.Defects in Solids. John Wiley & Sons, Chichester, 2008

    work page 2008

  56. [56]

    Hammond.The basics of crystallography and diffraction / Christopher Hammond.International Union of Crystallog- raphy texts on crystallography 5

    C. Hammond.The basics of crystallography and diffraction / Christopher Hammond.International Union of Crystallog- raphy texts on crystallography 5. Oxford University Press, New York, 2nd ed. edition, 2001

    work page 2001

  57. [57]

    The investigation of oxygen compounds of niobium in region of nbosub2– nbsub2o .Izv

    A Burdeze, E V Tkachenko, and F Abbattista. The investigation of oxygen compounds of niobium in region of nbosub2– nbsub2o .Izv. Akad. Nauk SSSR, Neorg. Mater. 5: 1957-62(Nov 1969)., 01 1969

    work page 1957

  58. [58]

    K. Sakata. The crystal structure of niobium dioxide.Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry, 35:2836–2841, 1979

    work page 1979

  59. [59]

    Complex permittivity of some ultralow loss dielectric crystals at cryogenic temperatures.Measurement Science and Technology, 10(5):387–392, 1999

    Jerzy Krupka, Krzysztof Derzakowski, Michael Tobar, John Hartnett, and Richard G Geyer. Complex permittivity of some ultralow loss dielectric crystals at cryogenic temperatures.Measurement Science and Technology, 10(5):387–392, 1999

    work page 1999

  60. [60]

    Chia-Jung Shih, Meng-Hung Tsai, Yu-Chen Chen, Yu-Ta Chen, Ming-Jen Li, Hung-Chi Yen, and Cheng-Liang Huang. Investigation of the dynamic interaction between dopants and oxygen vacancies in amorphous Nb 2O5: Simulation and experimental study.Materials Science and Engineering: B, 298:116891, 2023

    work page 2023

  61. [61]

    Dielectric properties of amorphous Nb 2O5 thin films.Thin Solid Films, 30(1):145–154, 1975

    N Fuschillo, B Lalevic, and NK Annamalai. Dielectric properties of amorphous Nb 2O5 thin films.Thin Solid Films, 30(1):145–154, 1975. 16 Appendix A: X-ray Diffraction To chemically characterize the Nb2O5 and NbO2 powders, we measured representative samples of each using XRD. Fig.8 shows the room-temperature diffraction patterns for both oxides. The presen...

    work page 1975