Low-Noise Microwave Squid Multiplexed Readout Of 38 X-Ray Transition-Edge Sensor Microcalorimeters

We report very-low-noise, fast-response, middle-scale multiplexing in a microwave superconducting quantum interference device multiplexer (MW-Mux) as a transition-edge sensor (TES) readout. Our MW-Mux is able to read 40 channels with 500 kHz sampling and has a low readout noise of 0.9 mu Phi(0)/root Hz (where Phi(0) is the magnetic flux quantum), equivalent to 9 pA/root Hz. By contrast, a multiplexer of less than 10 pixels with 500 kHz sampling and similar to 2 mu Phi(0)/root Hz readout noise has so far been reported in the literature. Owing to the 500 kHz sam- pling, our MW-Mux exhibits a fast response to detect a TES pulse with a rise time around 12 ps. We demonstrated simultaneous readout of 38 pixels from an array of x-ray TES microcalorimeters. The measured full-width values at half-maximum spectral resolution ranged from 2.79 to 4.56 eV, with a median value of 3.30 eV at 5.9 keV, including a similar to 10% contribution of readout noise, i.e., 0.9-1.7 eV. Published under license by AIP Publishing.