Measurement of MKID Performance with High-Speed and Wide-Band Readout System

Microwave kinetic inductance detectors (MKIDs) are being developed at the National Astronomical Observatory of Japan to enable precise measurements of the cosmic microwave background. One of the features of MKIDs is scalability using a frequency-division multiplexing (FDMUX) readout scheme. A digital fast fourier transform spectrometer (FFTS) is a good way to read out a number of resonance frequencies simultaneously and fully utilize the advantage of FDMUX of MKIDs. We have developed FFTS readout electronics using an ADC/DAC with 1 Gsps (sample per second) sampling rate and 270 MHz bandwidth. We measured the noise characteristics of a single MKID in the frequency range of 60 Hz–30 kHz with this readout system, and found the noise was almost equivalent to the noise measured by ordinary analog IQ down-converter readout. This indicates our FFTS electronics do not add any additional noise to the MKID readout system over the frequency range.