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PreprintarXiv licencearXiv

Phonon down-conversion by normal metals for superconducting devices

  • Guglielmo La Magna
  • Gianluigi Catelani
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Abstract

Thanks to low dissipation, superconducting devices are promising for a number of applications, such as detectors and implementations of quantum computation. However, their working can be adversely impacted by quasiparticles, which is why so-called quasiparticle poisoning mechanisms and their mitigation are under intense investigation. Here we focus on one poisoning mechanism, namely pair-breaking phonons, and its mitigation through down-conversion by a normal-metal film - the process in which scattering of high-energy phonons by electrons lowers the energy of the former below the pair-breaking threshold. To study the down-conversion, we introduce a model based on kinetic equations, which we solve both analytically (approximately) and numerically in the steady state. We use the solution to the estimate a properly-defined down-conversion efficiency which depends on material parameters (such as the strength of electron-phonon interaction and the phonon transmission coefficient at interfaces) and film and substrate thicknesses. Interestingly, we find that the efficiency is nearly optimal above a minimum metal thickness, typically between 50 and 500 nm depending on the metal-substrate combination.

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Cite

BibTeXRIS
BibTeX
@misc{magna2026phonon,
  title = {{Phonon down-conversion by normal metals for superconducting devices}},
  author = {Guglielmo La Magna and Gianluigi Catelani},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2607.13870},
  eprint = {2607.13870},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2607.13870},
}
RIS
TY  - UNPB
TI  - Phonon down-conversion by normal metals for superconducting devices
AU  - Guglielmo La Magna
AU  - Gianluigi Catelani
PY  - 2026
DA  - 2026/10/28
PB  - arXiv
DO  - 10.48550/arxiv.2607.13870
UR  - https://arxiv.org/abs/2607.13870
AB  - Thanks to low dissipation, superconducting devices are promising for a number of applications, such as detectors and implementations of quantum computation. However, their working can be adversely impacted by quasiparticles, which is why so-called quasiparticle poisoning mechanisms and their mitigation are under intense investigation. Here we focus on one poisoning mechanism, namely pair-breaking phonons, and its mitigation through down-conversion by a normal-metal film - the process in which scattering of high-energy phonons by electrons lowers the energy of the former below the pair-breaking threshold. To study the down-conversion, we introduce a model based on kinetic equations, which we solve both analytically (approximately) and numerically in the steady state. We use the solution to the estimate a properly-defined down-conversion efficiency which depends on material parameters (such as the strength of electron-phonon interaction and the phonon transmission coefficient at interfaces) and film and substrate thicknesses. Interestingly, we find that the efficiency is nearly optimal above a minimum metal thickness, typically between 50 and 500 nm depending on the metal-substrate combination.
ER  -