Resonance Spectra of Coplanar Waveguide MKIDs Obtained Using Frequency Sweeping Scheme

Abstract

We are developing a detector array for astronomical observations in the 100-GHz band using microwave kinetic inductance detectors (MKIDs) and a readout system for the array with frequency sweeping scheme, which uses a frequency sweeping probe signal instead of a fixed-frequency probe signal. This scheme enables us to simultaneously obtain the resonance spectra of MKIDs in an array and to derive the resonance frequencies corresponding to the power of incoming radiation. It has the advantage of the dynamic range being higher than the standard scheme and the derived resonance frequencies not being affected by changes of the gain or delay in the transmission line. The resonance profile measured, however, can be distorted by frequency sweeping, and hence, it is necessary to evaluate the effect of frequency sweeping on the resonance spectrum. We made measurements using the scheme with several frequency-sweep velocities and checked its effect on the resonance frequency and the quality factor. A slow frequency sweep causes only small differences in the resonance spectrum compared to an ideal profile, and hence suitable for astronomical applications.