Studies of the Effect of Crosstalk in Microwave Frequency Multiplexing Readout Systems for Cosmic Microwave Background Telescopes

Cutting-edge ground-based cosmic microwave background (CMB) telescopes must deploy tens of thousands of superconducting bolometers in order to measure distant light from the epoch of recombination. Reading out data from the high-density cryogenic focal planes which furnish these detectors to telescopes requires an effective multiplexing scheme. Microwave superconducting quantum interference device (SQUID) multiplexing has recently been deployed to the Simons Observatory, a new CMB research facility located at 5,200 m in Chile's Atacama Desert, to enable a multiplexing factor on the order of 1,000 for its 60,000 millimeter-wave detectors. Previous work has shown that while the crosstalk between neighboring channels read out via this novel multiplexing technology may be at the sub-percent level, it is nonlinear and time-variable, therefore introducing a potential bias and posing a technical challenge for its mitigation. This contribution will present simulations of this crosstalk effect in current-generation telescopes and discuss its impact on science results, including studies of reconstructing the weak lensing signal from the CMB, which is a powerful probe of large-scale structure.