CryoDE: A Digital Cryogenic Detector Emulator for Microwave SQUID Multiplexed Systems

Simultaneous readout of large-scale cryogenic detector arrays relies on multiplexing schemes such as the Frequency- Division Multiplexing (FDM) with microwave Superconducting Quantum Interference Device (SQUID) multiplexers and highly customized readout electronics. In traditional detector systems, where mixed-signal ASICs are used in detector frontends and typically provide a digital interface, Hardware-in-the- Loop (HIL) testing can be readily implemented by reusing the existing digital logic of the front-end for emulation purposes. Such straightforward emulation is not possible for FDM lowtemperature detectors, where the sensor signal is encoded in a high-frequency microwave carrier via a two-stage modulation scheme depending on the cryogenic resonators and the SQUID response. To address this challenge, we present CryoDE, a digital cryogenic-detector emulator for microwave SQUID multiplexed detector systems. CryoDE generates the encoded detector signals, including realistic pulse responses, enabling full HIL testing of the room-temperature DAQ system without requiring the cryogenic hardware. This resource-efficient FPGA-based detector twin integrates seamlessly into existing DAQ systems and allows experiment-specific adjustment of detector-signal parameters.We describe the internal architecture and capabilities of CryoDE within our custom HIL framework and demonstrate its use in evaluating the performance of real-time signal processing firmware optimized for different microwave SQUID multiplexed cryogenic-detector experiments.