Understanding Quality Factor Degradation in Superconducting Niobium Cavities at Low Microwave Field Amplitudes

Romanenko, Alexander; Schuster, David I.

doi:10.1103/physrevlett.119.264801

Cited by 82 publications

(89 citation statements)

References 36 publications

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“…A contribution by the natural oxide to residual resistance of some tenths of a nW would be consistent with the measurements presented here. An increase in residual resistance with oxide thickness is also consistent with measurements on anodized cavities in the relevant gradient range [28]. The reduced residual resistance may have also been due to the diffusion of impurities.…”

Section: Effect Of Surface Condition On Rf Performancesupporting

confidence: 84%

“…Additionally, there are non-accelerator applications requiring extremely high Q0 electromagnetic resonators where exposure to air after heat treatment is not needed or else where only a very brief exposure is needed (duration similar to that used for TE1PAV005). These include applications such as quantum computing [28], [35] and quantum sensors.…”

Section: Outlook: Future Improvement and Applicationsmentioning

confidence: 99%

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Ultralow Surface Resistance via Vacuum Heat Treatment of Superconducting Radio-Frequency Cavities

et al. 2020

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We report on an effort to improve the performance of superconducting radiofrequency cavities by the use of heat treatment in a temperature range sufficient to dissociate the natural surface oxide. We find that the residual resistance is significantly decreased, and we find an unexpected reduction in the BCS resistance. Together these result in extremely high quality factor values at relatively large accelerating fields Eacc ~20 MV/m: Q0 of 3-4´10 11 at <1.5 K and Q0 ~5´10 10 at 2.0 K. In one cavity, measurements of surface resistance versus temperature showed an extremely small residual resistance of just 0.63 ± 0.06 nW at 16 MV/m. SIMS measurements confirm that the oxide was significantly dissociated, but they also show the presence of nitrogen after heat treatment. We also present studies of surface oxidation via exposure to air and to water, as well as the effects of very light surface removal via HF rinse. The possibilities for applications and the planned future development are discussed.

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Section: Effect Of Surface Condition On Rf Performancesupporting

confidence: 84%

Section: Outlook: Future Improvement and Applicationsmentioning

confidence: 99%

Ultralow Surface Resistance via Vacuum Heat Treatment of Superconducting Radio-Frequency Cavities

et al. 2020

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“…(6): G R = (ǫ + iΓ)/ (ǫ + iΓ) 2 + ∆ 2 and F R = ∆/ (ǫ + iΓ) 2 + ∆ 2 . Then Eq (7). reproduces the Dynes formula[2,22]…”

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confidence: 75%

Weak-field dissipative conductivity of a dirty superconductor with Dynes subgap states under a dc bias current up to the depairing current density

Kubo

2020

Phys. Rev. Research

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We study the dissipative conductivity σ1 of a dirty superconductor with a finite Dynes parameter Γ under a dc-biased weak time-dependent field. The Usadel equation for the current-carrying state is solved to calculate the pair potential, penetration depth, supercurrent density, and quasiparticle spectrum. It is shown that, while the depairing current density j d for Γ = 0 is coincident with the Kupriyanov-Lukichev theory, a finite Γ decreases the superfluid density, resulting in a reduction of j d . The broadening of the peaks of the quasiparticle density of states induced by a combination of a finite Γ and a dc bias can reduce σ1 below that for the ideal dirty BCS superconductor with Γ = 0, while subgap states at Fermi level proportional to Γ results in a residual conductivity at T → 0. We find the optimum combination of Γ and the dc bias to minimize σ1 by scanning all Γ and all currents up to j d . By using the results, it is possible to improve j d and reduce electromagnetic dissipation in various superconducting quantum devices.

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“…The simulation parameters for the constituent materials are as follows: the SA interface is modelled as a 5 nm thick layer of SiO 2 [41] with relative permittivity ε r (SiO 2 ) = 4.2. The MA interface consists of a 5 nm thick layer of Nb 2 O 5 [42] with relative permittivity ε r (Nb 2 O 5 ) = 33 [43,44]. The SM interface is modelled by a 2 nm thick layer inside the substrate (ε r (SM) = ε r (Si) = 11.7) [28].…”

Section: Filling Factor Simulationsmentioning

confidence: 99%

Geometric scaling of two-level-system loss in superconducting resonators

Niepce

Burnett

Latorre

et al. 2020

Supercond. Sci. Technol.

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We perform an experimental and numerical study of dielectric loss in superconducting microwave resonators at low temperature. Dielectric loss, due to two-level systems, is a limiting factor in several applications, e.g. superconducting qubits, Josephson parametric amplifiers, microwave kineticinductance detectors, and superconducting single-photon detectors. Our devices are made of disordered NbN, which, due to magnetic-field penetration, necessitates 3D finite-element simulation of the Maxwell-London equations at microwave frequencies to accurately model the current density and electric field distribution. From the field distribution, we compute the geometric filling factors of the lossy regions in our resonator structures and fit the experimental data to determine the intrinsic loss tangents of its interfaces and dielectrics. We emphasise that the loss caused by a spin-on-glass resist such as hydrogen silsesquioxane (HSQ), used for ultrahigh lithographic resolution relevant to the fabrication of nanowires, and find that, when used, HSQ is the dominant source of loss, with a loss tangent of δ i HSQ = 8 × 10 −3 .

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Understanding Quality Factor Degradation in Superconducting Niobium Cavities at Low Microwave Field Amplitudes

Cited by 82 publications

References 36 publications

Ultralow Surface Resistance via Vacuum Heat Treatment of Superconducting Radio-Frequency Cavities

Ultralow Surface Resistance via Vacuum Heat Treatment of Superconducting Radio-Frequency Cavities

Weak-field dissipative conductivity of a dirty superconductor with Dynes subgap states under a dc bias current up to the depairing current density

Geometric scaling of two-level-system loss in superconducting resonators

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