A High-Capacity Microwave SQUID Multiplexer Chip Screening System

The microwave SQUID multiplexer (μMUX) is a high channel-count multiplexer that, when coupled to low-temperature detectors such as Transition Edge Sensor (TES) Bolometers, has applications across astronomy and physics. Our primary application is for the Simons Observatory, an array of CMB polarimeters utilizing over 70,000 μMUX readout channels, located in the Atacama Desert. To facilitate the delivery of high-quality multiplexers to the project, we have developed a high-throughput microwave SQUID screening measurement system, capable of measuring microwave devices operating over the frequency range of 4-8 GHz. Here, we present the hardware design comprised of a cryogen-free 100 mK 2-stage Adiabatic Demagnetization Refrigerator (ADR) cryostat, microwave packages which hold μ MUX chips, and the microwave readout chain necessary to do these measurements. In addition, we describe the screening protocols and show example results.