Selected Publications

Demonstration of a scalable frequency-domain readout of metallic magnetic calorimeters by means of a microwave SQUID multiplexer

S. Kempf, M. Wegner, A. Fleischmann, L. Gastaldo, F. Herrmann, M. Papst, D. Richter, C. Enss

We report on the first demonstration of a scalable GHz frequency-domain readout of metallic magnetic calorimeters (MMCs) using a 64 pixel detector array that is read out by an integrated, on-chip microwave SQUID multiplexer. The detector array is optimized for detecting soft X-ray photons and the multiplexer is designed to pro- vide a signal rise time τrise < 400 ns and an intrinsic energy sensitivity ε < 30 h. This results in an expected energy resolution EFWHM < 10 eV . We measured a signal rise time τrise as low as 90 ns and an energy resolution EFWHM as low as 50 eV for 5.9 keV photons. The rise time is about an order of magnitude faster compared to other multiplexed low-temperature microcalorimeters and close to the intrinsic value set by the coupling between electron and spins. The energy resolution is degraded with respect to our design value due to a rather low intrinsic quality factor of the microwave resonators that is caused by the quality of the Josephson junction of the associated rf-SQUID as well as an elevated chip temperature as compared to the heat bath. Though the achieved energy resolution is not yet compatible with state-of- the-art single-channel MMCs, this demonstration of a scalable readout approach for MMCs in combination with the full understanding of the device performance showing ways how to improve represents an important milestone for the development of future large-scale MMC detector arrays. 

AIP Advances 7 (2017) 015007

doi: 10.1063/1.4973872