Magnetic Field Sensitivity of Microwave SQUID Multiplexers

We present magnetic field sensitivity measurements of microwave SQUID multiplexers designed for bolometric applications. These devices are often used in environments with changing external magnetic fields, due to either motion through Earth’s field or radiation from other pieces of instrumentation. To minimize the pickup of magnetic fields, these multiplexers utilize gradiometric SQUIDs, but residual pickup remains and must be characterized in order to design adequate magnetic shielding for a given application. To study the perpendicular field response, we utilize a single-axis cryogenic Helmholtz coil mounted to the mixing chamber of a dilution refrigerator, calibrated with a cryogenic fluxgate magnetometer. Measurements were made on multiplexer devices across varying microwave readout frequencies for AC magnetic fields from 0.01 to 100 Hz. We measure the magnetic field sensitivity of the multiplexer devices to be 0.1–0.3 ϕ _0 /Gauss, equivalent to an effective area of gradiometric failure of 2–6 μm ^2 .Please check if the corresponding author affiliation is correctly identified.This looks correct to me.