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Microwave SQUID Multiplexer for the Readout of Metallic Magnetic Calorimeters


We have realized a frequency-domain multiplexing technique for the readout of large metallic magnetic calorimeter detector arrays. It is based on non-hysteretic single-junction SQUIDs and allows for a simultaneous readout of hundreds or thousands of detectors by using a single cryogenic high electron mobility transistor amplifier and two coaxial cables that are routed from room-temperature to the detector array. We discuss the working principle of the multiplexer and present details about our prototype multiplexer design. We show that fabricated devices are fully operational and that characteristic SQUID parameters such as the input sensitivity of the SQUID or the resonance frequency of the readout circuit can be predicted with confidence. Our best device so far has shown a magnetic flux white noise level of 1.4 m\({\Phi _0}/\sqrt{Hz}\) which can in future be reduced by an optimization of the fabrication processes as well as an improved microwave readout system.

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We are deeply grateful to J. Beyer, G. C. Hilton, J. A. B. Mates, L. R. Vale, and K. D. Irwin for many valuable discussions. We also would like to thank T. Wolf for technical support during device fabrication. This work was supported by the BMBF Grant 06 HD 9118I, the GSI R&D grant HDEnss, and the European Community Research Infrastructures under the FP7 Capacities Specific Programme, MICROKELVIN Project Number 228464.

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Kempf, S., Gastaldo, L., Fleischmann, A. et al. Microwave SQUID Multiplexer for the Readout of Metallic Magnetic Calorimeters. J Low Temp Phys 175, 850–860 (2014).

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  • Microwave SQUID based MMC multiplexer
  • Metallic magnetic calorimeters
  • Frequency-domain multiplexing
  • Non-hysteretic single-junction SQUIDs
  • SQUID characterization