Development of Microwave Kinetic Inductance Detector and its Readout System for LiteBIRD

We have developed a microwave kinetic inductance detector (MKID) and its readout system for the satellite LiteBIRD (Light satellite for the studies of B-mode polarization and Inflation from cosmic background Radiation Detection). Primordial gravitational waves generated by inflation have produced an odd-parity pattern B-mode in the cosmic microwave background (CMB) polarization. LiteBIRD aims at detecting this B-mode polarization precisely. It requires about 2000 detectors capable of detecting a frequency range from 50 to 250 GHz with ultra low noise. Superconductive detectors are suitable for this requirement. We have fabricated and tested an MKID and its readout system. We have designed an antenna-coupled MKID. Quasi-particles are created by incident radiation and are detected as a change of the surface impedance of a superconductor strip. This change of the surface impedance is translated to the change of the resonant frequency of a microwave signal transmitted through the resonator. We also have developed a new readout system for an MKID. An MKID can detect signals with a wide dynamic range, and can be multiplexed in a single readout line. The commonly used readout system that monitors the amplitude and phase at a certain resonant frequency is not suitable for LiteBIRD that requires a large dynamic range. We have developed a new readout system capable of tracking the resonant frequency change based on the phase monitoring. We report the recent R&D status of developing a MKID and its readout system for LiteBIRD.