Digital frequency multiplexing with sub-Kelvin SQUIDs

TL;DR

This paper discusses the development of a sub-Kelvin SQUID architecture for digital frequency multiplexed bolometers, aiming to improve noise performance and scalability for future large-scale cosmic microwave background experiments.

Contribution

It introduces a novel SQUID placement at the detector stage, enhancing electrical performance and enabling higher multiplexing factors in CMB detector arrays.

Findings

Potential for lower noise operation.

Increased multiplexing capabilities.

Reduced wiring parasitics.

Abstract

Digital frequency multiplexing (dfMux) is a readout architecture for transition edge sensor-based detector arrays and is used on telescopes including SPT-3G, POLARBEAR-2, and LiteBIRD. Here, we present recent progress and plans for development of a sub-Kelvin SQUID architecture for digital frequency multiplexed bolometers. This scheme moves the SQUID from the 4 K stage to the 250 mK stage, adjacent to the bolometers. Operating the SQUID on the detector stage may offer lower noise and greater scalability. Electrical performance will be improved as a result of decreased wiring length and reduced parasitics, allowing for higher multiplexing factors and lower bolometer R_normal . These performance improvements will enable ultra-large focal planes for future instruments such as CMB-S4.