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arxiv: 2604.19322 · v1 · submitted 2026-04-21 · 🪐 quant-ph · cond-mat.mes-hall

Thermal-fluctuator driven decoherence of an oscillator resonantly coupled to a two-level system

Thomas J. Antolin , Jonas Glatthard , Andrew D. Armour This is my paper

Pith reviewed 2026-05-10 02:31 UTC · model grok-4.3

classification 🪐 quant-ph cond-mat.mes-hall
keywords decoherencetwo-level systemsthermal fluctuatorsquantum oscillatorscoherence decayRabi oscillationssuperconducting resonators
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The pith

Bath-driven transitions in a thermally activated two-level fluctuator cause irreversible coherence decay in an oscillator coupled to a near-resonant two-level system.

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

The paper models an oscillator resonantly coupled to a two-level system and shows how its coherence is degraded by interactions with lower-frequency thermally activated two-level fluctuators. Transitions in a single fluctuator, driven by a thermal bath, produce irreversible decay whose rate depends sharply on the coupling strengths and the fluctuator's transition rate; this decay can appear together with or replace ordinary Rabi oscillations. For an ensemble of fluctuators the oscillator exhibits distinct regimes of non-exponential decay arising from phase averaging, and numerical checks reveal how small numbers of fluctuators deviate from the continuum limit. These results supply a framework for treating the combined effects of coherent two-level-system interactions and fluctuator-induced dephasing in devices such as superconducting or phononic resonators.

Core claim

Bath-driven transitions in the TLF cause irreversible coherence decay at a rate that is highly sensitive to both the couplings and the transition rate. For an ensemble of TLFs, different regimes of non-exponential phase-averaging-driven coherence decay appear, and numerical calculations show the extent to which systems with just a few TLFs differ from the large-ensemble limit.

What carries the argument

Bath-driven transitions in the TLF that produce irreversible coherence decay, together with phase averaging over an ensemble of TLFs.

If this is right

  • A single TLF can generate coherence oscillations that coexist with or replace the Rabi oscillations of the oscillator-TLS system.
  • The irreversible decay rate depends sensitively on both the oscillator-TLF and TLF-TLS coupling strengths.
  • An ensemble of TLFs produces distinct non-exponential decay regimes governed by phase averaging.
  • Systems containing only a few TLFs can deviate measurably from the continuum-ensemble limit, as quantified by numerical calculations.

Where Pith is reading between the lines

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

  • Device coherence times in superconducting resonators could be improved by engineering TLF transition rates or by reducing the relevant coupling strengths.
  • Temperature-dependent measurements of decay rates would directly test the predicted sensitivity to TLF transition rates.
  • The same TLF-induced mechanism may set limits on coherence in other hybrid quantum systems that combine oscillators with TLSs.

Load-bearing premise

The dominant source of decoherence is the specified couplings to thermally activated TLFs with given transition rates, without significant contributions from other unmodeled noise sources.

What would settle it

Experimental measurement of the oscillator's coherence decay rate as a function of the TLF transition rate (for example by varying temperature) that fails to show the predicted strong sensitivity or that remains purely exponential rather than displaying the calculated non-exponential regimes.

Figures

Figures reproduced from arXiv: 2604.19322 by Andrew D. Armour, Jonas Glatthard, Thomas J. Antolin.

Figure 1
Figure 1. Figure 1: (a) Evolution of the oscillator coherence C(t) for a single weakly coupled TLF in the scale-separated limit (p± = 1/2). Different curves compare the full expression (equation (12), black) and the weak-coupling approximation (equation (14), blue). (b) Evolution of the weak-coupling TLF-induced envelope CTLF(t), obtained using equation (14), for different temperatures. We set εT /ω0 = 1.01, ε/ω0 = 0.1, g/ω0 … view at source ↗
Figure 2
Figure 2. Figure 2: Evolution of C(t) with a single strongly coupled non-dissipative fluctuator in the scale-separated limit (p± = 1/2) with: i) g/λ = 0.3, ii) g/λ = 0.2 and iii) g/λ = 0.1. (a) Comparison of the full expression (equation (12), black lines), and the approximate expression for the strongly coupled TLF envelope (equation (15), blue lines). (b) Behaviour over a narrower time window, here the higher order expressi… view at source ↗
Figure 3
Figure 3. Figure 3: Evolution of C(t) with a single dissipative TLF in the scale-separated limit (p± = 1/2) for varying γ/λ. (a) Comparison for a weakly-coupled TLF (g ≫ |λ|) of the numerically solved master equation (equation (C.1), black dashed/solid lines), and the approximate expression (equation (16), red/blue). (b) Comparison for a strongly-coupled TLF (g ≪ |λ|) of the numerically solved master equation (equation (C.1),… view at source ↗
Figure 4
Figure 4. Figure 4: Evolution of C(t) for a narrow ensemble (g ≫ σ) of (a) 5, (b) 10, and (c) 15 TLFs in the scale-separated limit (p±,j = 1/2, ∀j) with σ/g = 0.084, 0.102 and 0.105, respectively. In each case, the exact solution (equation (21), red) is compared with the approximate expression (equation (29), black) and the envelope, CTLF(t) = exp(−σ 2 t 2/2) (blue). We set δ = 0, g/ω0 = 0.1 and sampled the TLS–TLF couplings … view at source ↗
Figure 5
Figure 5. Figure 5: Evolution of C(t) for a narrow ensemble (g ≫ σ) of 15 TLFs in the scale￾separated limit (p±,j = 1/2, ∀j). (a), (b) and (c) are three different samplings of TLS– TLF couplings from a uniform random distribution of locations in a two-dimensional substrate (see text for details), leading to σ/g = 0.093, 0.23 and 0.24, respectively. The corresponding R = max(σ 2 j )/σ2 values are (a) 0.22, (b) 0.45 and (c) 0.9… view at source ↗
Figure 6
Figure 6. Figure 6: Evolution of C(t) for a broad ensemble (σ ≫ g) of (a) 5, and (b) 15 TLFs in the scale-separated limit (p±,j = 1/2, ∀j). In each case, a single realisation of a uniform random coupling distribution (green) is compared with three samples from a random distribution of locations (blue), details of which are given in the main text, and equation (30) (red). We set δ = 0, g/ω0 = 0.01 and the uniform random distri… view at source ↗
Figure 7
Figure 7. Figure 7: (a) Short time approximations to C(t) in the broad-ensemble (σ ≫ g) and scale-separated (p±,j = 1/2, ∀j) regimes. Approximations for intermediate (t ≲ σ/g2 , equation (31), red) and short (t ≪ σ/g2 , equation (32), dashed green line) times are shown together with the large-ensemble approximation (equation (26), blue). (b) C(t) in the large-ensemble limit, equation (26), for varying µ/σ. We set δ = 0 and g/… view at source ↗
read the original abstract

Recent experiments on a range of engineered quantum systems have highlighted the important role of interacting two-level systems (TLSs) in modifying device properties and generating fluctuations. Focusing on the case of an oscillator coupled to a single near-resonant TLS, we explore how interactions between the TLS and lower-frequency thermally activated two-level fluctuators (TLFs) degrade the oscillator's coherence. Depending on the strength of the couplings, a single TLF can give rise to coherence oscillations that appear alongside, or supplant, Rabi oscillations of the oscillator-TLS system. Bath-driven transitions in the TLF cause irreversible coherence decay at a rate that is highly sensitive to both the couplings and the transition rate. For an ensemble of TLFs, we identify and characterise the different regimes of non-exponential phase-averaging-driven coherence decay that the oscillator can display. Using numerical calculations, we examine the extent to which systems with just a few TLFs differ from the limit of a large (continuum) TLF ensemble. Our work provides a theoretical framework for understanding the interplay of coherent TLS interactions and TLF-induced dephasing in quantum devices such as superconducting and phononic resonators.

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

0 major / 3 minor

Summary. The manuscript investigates decoherence of an oscillator resonantly coupled to a two-level system (TLS) arising from interactions with lower-frequency thermally activated two-level fluctuators (TLFs). Numerical calculations show that a single TLF can produce coherence oscillations alongside or instead of Rabi oscillations, while bath-driven TLF transitions induce irreversible coherence decay whose rate depends sensitively on the couplings and TLF transition rate. For an ensemble of TLFs the work identifies and characterizes distinct regimes of non-exponential, phase-averaging-driven decay and compares the few-TLF case to the continuum limit, providing a framework relevant to superconducting and phononic resonators.

Significance. If the numerical results hold, the paper supplies a timely theoretical framework for TLF-induced dephasing in engineered quantum systems where TLS-TLF interactions are known to affect device performance. The explicit mapping of parameter regimes (coupling strengths, transition rates) to qualitative decay behaviors, together with the few-versus-continuum comparison, offers concrete guidance for experiment design and data interpretation. The reliance on direct numerical integration of the open-system dynamics is a clear strength that allows exploration of non-Markovian and non-exponential features without additional approximations.

minor comments (3)
  1. [Numerical methods section] The numerical method (likely a stochastic Liouville or master-equation integrator) is described only at a high level; adding a brief statement on integrator type, time-step convergence tests, and ensemble averaging procedure would improve reproducibility.
  2. [Figure captions] Several figure captions omit the precise values of the TLF transition rate and coupling strengths used in each panel, forcing the reader to cross-reference the main text repeatedly.
  3. [Ensemble TLF analysis] The definition of the phase-averaging procedure for the ensemble case could be stated more explicitly (e.g., whether it is an average over static TLF configurations or a dynamical average over transition trajectories).

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive assessment of our manuscript, accurate summary of the key results, and recommendation for minor revision. The significance statement correctly identifies the relevance to superconducting and phononic resonators and the value of the numerical approach for capturing non-Markovian and non-exponential features.

Circularity Check

0 steps flagged

No significant circularity; derivation self-contained via standard open-system modeling

full rationale

The paper's central claims rest on a standard treatment of an oscillator coupled to a TLS with additional TLFs, using master-equation or stochastic methods to derive coherence decay rates and regimes from the Hamiltonian couplings and transition rates. Numerical calculations distinguish few-TLF vs continuum limits without reducing any prediction to a fitted input or self-referential definition. No load-bearing self-citations, ansatz smuggling, or uniqueness theorems from prior author work are invoked in the abstract or described framework; the sensitivity to couplings and non-exponential phase-averaging follow directly from averaging over the TLF parameters as independent inputs. The analysis is externally falsifiable via the stated assumptions and numerics.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

The model rests on standard open-quantum-system assumptions plus parameters for couplings and TLF transition rates; no new entities are postulated.

free parameters (2)
  • coupling strengths between TLF, TLS, and oscillator
    These determine whether coherence shows oscillations or irreversible decay and are treated as variable inputs.
  • TLF transition rate
    The bath-driven switching rate controls the irreversible decay speed and is a key tunable parameter.
axioms (2)
  • standard math Resonant coupling between oscillator and TLS can be treated within standard quantum mechanics
    The setup begins from the resonant oscillator-TLS interaction without deriving it from more fundamental principles.
  • domain assumption TLFs are thermally activated at lower frequencies and interact via the described couplings
    The paper assumes this is the dominant mechanism for the observed decoherence.

pith-pipeline@v0.9.0 · 5519 in / 1468 out tokens · 36376 ms · 2026-05-10T02:31:27.313802+00:00 · methodology

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Reference graph

Works this paper leans on

36 extracted references · 36 canonical work pages

  1. [1]

    Low Temp

    Phillips W A 1972J. Low Temp. Phys.7351

    work page

  2. [2]

    Anderson P W, Halperin B I and Varma C M 1972Phil. Mag.251

    work page

  3. [3]

    Phillips W A 1987Rep. Prog. Phys501657

    work page

  4. [4]

    Hunklinger S 1988Cryogenics28224

    work page

  5. [5]

    Stephens R B and Liu X 2021Low-Energy Excitations in Disordered Solids (Singapore: World Scientific)

    work page

  6. [6]

    Paladino E, Faoro L, Falci G and Fazio R 2002Phys. Rev. Lett.88228304

    work page

  7. [7]

    Galperin Y M, Altshuler B, Bergli J and Shantsev D 2006Phys. Rev. Lett.96 097009

    work page

  8. [8]

    Phys.11025002

    Bergli J, Galperin Y M and Altshuler B 2009New J. Phys.11025002

    work page

  9. [9]

    Paladino E, Galperin Y, Falci G and Altshuler B 2014Rev. Mod. Phys.86361–418

    work page

  10. [10]

    Matityahu S, Shnirman A, Schön G and Schechter M 2016Phys. Rev. B93134208

    work page

  11. [11]

    Müller C, Cole J H and Lisenfeld J 2019Rep. Prog. Phys.82124501

    work page

  12. [12]

    Simmonds R W, Lang K M, Hite D A, Nam S, Pappas D P and Martinis J M 2004 Phys. Rev. Lett.93077003

    work page 2004

  13. [13]

    Commun.66182

    Lisenfeld J, Grabovskij G J, Müller C, Cole J H, Weiss G and Ustinov A V 2015 Nat. Commun.66182

    work page 2015

  14. [14]

    Müller C, Lisenfeld J, Shnirman A and Poletto S 2015Phys. Rev. B92035442

    work page

  15. [15]

    Commun.54119

    Burnett J, Faoro L, Wisby I, Gurtovoi V L, Chernykh A V, Mikhailov G M, Tulin V A, Shaikhaidarov R, Antonov R V, Meeson P J, Tzalenchuk A Y and Lindström T 2014Nat. Commun.54119

    work page

  16. [16]

    Faoro L and Ioffe L B 2015Phys. Rev. B91014201

    work page

  17. [17]

    Béjanin J H, Earnest C T, Sharafeldin A S and Mariantoni M 2021Phys. Rev. B 104094106

    work page

  18. [18]

    Commun.126182

    Cattiaux D, Golokolenov I, Kumar S, Sillanpää M, Mercier de Lépinay L, Gazizulin R R, Zhou X, Armour A D, Bourgeois O, Fefferman A and Collin E 2021Nat. Commun.126182

    work page

  19. [19]

    Commun.154979

    Cleland A Y, Wollack E and Safavi-Naeini A 2024Nat. Commun.154979

    work page

  20. [20]

    Bozkurt A B, Golami O, Yu Y, Tian H and Mirhosseini M 2025Nature Physics21 1469

    work page

  21. [21]

    Yuksel M, Maksymowych M, Hitchcock O, Mayor F, Lee N, Dykman M, Safavi- Naeini A and Roukes M 2025arXiv2502.18587

    work page arXiv

  22. [22]

    Carruzzo H M and Yu C C 2020Phys. Rev. Lett.124075902

    work page

  23. [23]

    Maksymowych M, Yuksel M, Hitchcock O, Lee N, Mayor F, Jiang W, Roukes M and Safavi-Naeini A 2025Phys. Rev. Appl.24044066

    work page

  24. [24]

    Matityahu S, Shnirman A and Schechter M 2024Phys. Rev. Appl.21044055 REFERENCES24

    work page

  25. [25]

    Jaynes E T and Cummings F W 2005Proceedings of the IEEE5189

    work page

  26. [26]

    Garrison J and Chiao R 2008Quantum Optics(Oxford: Oxford University Press)

    work page

  27. [27]

    Wang Y and Haw J Y 2015Physics Letters A379779

    work page

  28. [28]

    Remus L G, Blencowe M P and Tanaka Y 2009Phys. Rev. B80174103

    work page

  29. [29]

    Remus L G and Blencowe M P 2012Phys. Rev. B86205419

    work page

  30. [30]

    Walls D F and Milburn G J 1985Phys. Rev. A312403

    work page

  31. [31]

    Haroche S and Raimond J M 2006Exploring the Quantum: Atoms, Cavities, and Photons(Oxford: Oxford University Press)

    work page

  32. [32]

    Billingsley P 1995Probability and Measure3rd ed (Hoboken: John Wiley & Sons)

    work page

  33. [33]

    Behunin R O, Intravaia F and Rakich P T 2016Phys. Rev. B93224110

    work page

  34. [34]

    Lisenfeld J, Bilmes A, Matityahu S, Zanker S, Marthaler M, Schechter M, Schön G, Shnirman A, Weiss G and Ustinov A V 2016Scientific Reports623786

    work page

  35. [35]

    Hitchcock O A, Mayor F M, Jiang W, Maksymowych M P, Malik S and Safavi- Naeini A H 2026Phys. Rev. Appl.25024005

    work page

  36. [36]

    Phys.21 113045

    Cattaneo M, Giorgi G L, Maniscalco S and Zambrini R 2019New J. Phys.21 113045

    work page