The SQUID Controller Unit for the LiteBIRD Space Mission: Description, Functional Tests and Early Performance Assessment

LiteBIRD is a satellite mission to be launched by JAXA in the early 2030s. It will measure the Cosmic Microwave Background (CMB) primordial B-modes with an unprecedented sensitivity. Microwave radiation will be detected by Transition Edge Sensors (TESs) arrays multiplexed in frequency domain and read by Superconducting QUantum Interference Devices (SQUIDs). The LiteBIRD SQUID Controller Unit (SCU), based on the heritage of the successful design used for the ground-based SPT3G experiment, presents some novel elements that make it suitable for a space-borne application. We compare our first breadboard model with the ground-based, Off-The-Shelf Components (COTS) version, by driving the same SQUID Array Amplifier (SAA) at 4 K, measuring relevant quantities such as noise, gain and bandwidth. We demonstrate that the noise added by our first prototype (including a switching part for redundancy purposes) never exceeds the noise added by the COTS-based electronics board, representing our benchmark. We also present the first noise estimates with the SAA cooled below 1 K, going closer to the conditions expected for LiteBIRD operation.