Kinetic inductance detectors (KIDs) are a promising new technology first proposed in 2003, based on superconducting resonators. Its features are ultra-high sensitivity, high quality factor (Q>105), wideband, easy fabrication and the possibility it offers in multiplexing large detector arrays. It has been applied in various astronomical projects from millimeter, infrared, and optical bands to X-rays, passive imaging and single photon counting.
KIDs work at a temperature much lower than the critical temperature of their material, making use of the change in the surface impedance of a superconductor as the incoming photons break up Cooper pairs. The change in surface impedance shifts the resonance frequency changing the phase of the resonator. The incoming signal can be detected by measuring such phase change. KIDs arrays can be easily made by tuning their resonance frequency and readout by a single coaxial cable.
The goal of this lecture is to introduce the physics of KIDs, including their working principle, noise, design, and characterization. The basics of KIDs theory will be presented and their design and characterization will be discussed. Current applications will also be reviewed.