A microwave SQUID multiplexing concept for macro-cryogenic calorimeter arrays

Abstract

Massive cryogenic calorimeters read out by transition-edge sensors (TES) can reach eV-scale baseline resolution, but the single-channel dc-SQUID readout conventionally used in rare-event searches, with one amplifier chain and several wires per detector, limits practical arrays to a few tens of channels. We propose to apply microwave SQUID multiplexing (μMUX), developed for fast X-ray and neutrino-mass microcalorimeters, to massive BGO (Bi₄Ge₃O₁₂) calorimeters operated at ≃ 20~mK; sapphire and TeO₂ absorbers are covered by the same framework. Using the established thermal and noise model for massive TES calorimeters, we derive a noise model for the multiplexed readout, including the HEMT, two-level-system and SQUID contributions, and its scaling with the multiplexing factor N_mux. Since the slow thermal signals require only about a kHz of sampling per channel, the limiting requirement is not bandwidth but an input-coil sensitivity of $( 0.1$ to 1) μA/Φ₀, a factor of $10$ to $30$ beyond current μMUX devices, matched to the detector current noise of ($9$ to $10) pA/\sqrt{\rm Hz}$, which is independent of the absorber mass. With a total flux noise of ≃1.2 μΦ₀/√(Hz), the readout degrades the baseline resolution by less than 2% up to N_mux=1000, negligible compared with the TES-limited resolution. These results are implemented in a single-tower design: 52 BGO crystals of 100~g each and one HEMT amplifier. The tower is the unit of a multi-tower array of several kilograms aimed at CEνNS and dark matter searches.

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BibTeX RIS

BibTeX

@misc{iachellini2026microwave,
  title = {{A microwave SQUID multiplexing concept for macro-cryogenic calorimeter arrays}},
  author = {N. Ferreiro Iachellini and P. Szypryt and L. Canonica and W. B. Doriese and M. Durkin and A. Giachero and J. A. B. Mates and A. Nucciotti and L. Pattavina and S. Quitadamo and C. Shiu and J. N. Ullom and M. R. Vissers},
  howpublished = {arXiv},
  year = {2026},
  month = aug,
  doi = {10.48550/arxiv.2608.27556},
  eprint = {2608.27556},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2608.27556},
}

RIS

TY  - UNPB
TI  - A microwave SQUID multiplexing concept for macro-cryogenic calorimeter arrays
AU  - N. Ferreiro Iachellini
AU  - P. Szypryt
AU  - L. Canonica
AU  - W. B. Doriese
AU  - M. Durkin
AU  - A. Giachero
AU  - J. A. B. Mates
AU  - A. Nucciotti
AU  - L. Pattavina
AU  - S. Quitadamo
AU  - C. Shiu
AU  - J. N. Ullom
AU  - M. R. Vissers
PY  - 2026
DA  - 2026/08/27
PB  - arXiv
DO  - 10.48550/arxiv.2608.27556
UR  - https://arxiv.org/abs/2608.27556
AB  - Massive cryogenic calorimeters read out by transition-edge sensors (TES) can reach eV-scale baseline resolution, but the single-channel dc-SQUID readout conventionally used in rare-event searches, with one amplifier chain and several wires per detector, limits practical arrays to a few tens of channels. We propose to apply microwave SQUID multiplexing (μMUX), developed for fast X-ray and neutrino-mass microcalorimeters, to massive BGO (Bi_4Ge_3O_12) calorimeters operated at ≃ 20~mK; sapphire and TeO_2 absorbers are covered by the same framework. Using the established thermal and noise model for massive TES calorimeters, we derive a noise model for the multiplexed readout, including the HEMT, two-level-system and SQUID contributions, and its scaling with the multiplexing factor N_mux. Since the slow thermal signals require only about a kHz of sampling per channel, the limiting requirement is not bandwidth but an input-coil sensitivity of $( 0.1$ to 1) μA/Φ_0, a factor of $10$ to $30$ beyond current μMUX devices, matched to the detector current noise of ($9$ to $10) pA/\sqrt{\rm Hz}$, which is independent of the absorber mass. With a total flux noise of ≃1.2 μΦ_0/√(Hz), the readout degrades the baseline resolution by less than 2% up to N_mux=1000, negligible compared with the TES-limited resolution. These results are implemented in a single-tower design: 52 BGO crystals of 100~g each and one HEMT amplifier. The tower is the unit of a multi-tower array of several kilograms aimed at CEνNS and dark matter searches.
ER  -

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