Bandwidth and Aliasing in the Microwave SQUID Multiplexer

The microwave SQUID multiplexer ( μ mux) has enabled higher bandwidth or higher channel counts across a wide range of experiments in particle physics, astronomy, and spectroscopy. The large multiplexing factor coupled with recent commercial availability of microwave components and warm electronics readout systems make it an attractive candidate for systems requiring large cryogenic detector counts. Since the multiplexer is considered for both bolometric and calorimetric applications across several orders of magnitude of signal frequencies, understanding the bandwidth of the device and its interaction with readout electronics is key to appropriately designing and engineering systems. Here, we discuss several important factors contributing to the bandwidth properties of μ mux systems, including the intrinsic device bandwidth, interactions with warm electronics readout systems, and aliasing. We present simulations and measurements of μ mux devices coupled with SLAC Microresonator RF (SMuRF) tone-tracking electronics and discuss several implications for future experimental design.