Readout of X-ray Pulses from a Single-pixel TES Microcalorimeter with Microwave Multiplexer Based on SQUIDs Directly Coupled to Resonators

We have first demonstrated the cooperation between an X-ray TES and a directly coupled microwave SQUID multiplexer (D-coup. MW-Mux) in which SQUIDs are directly coupled to resonators. Using D-coup. MW-Mux, we successfully detected the X-ray pulses from a single-pixel TES and evaluated the energy resolution of 11.8 eV FWHM at 5.9 keV. We found this preliminary energy resolution is attributed to non-optimum bias point of the present TES, which can be improved by the future reduction of readout noise.