Visible to Near-Infrared Kinetic Inductance Detectors

Abstract

Kinetic inductance detectors (KIDs) are superconducting resonators whose resonance condition strongly depends on the properties of a thin superconducting film. Below the critical temperature of the superconducting film, most of the electrons have paired up into Cooper pairs, which give rise to a kinetic inductance. The remaining excitations are a mix of electrons and holes, which can be described as quasiparticles and lead to microwave loss. The resonator’s resonance frequency then depends on the Cooper pair density, while the resonator’s internal loss depends on the quasiparticle density. When the resonator is exposed to a photon flux of sufficient energy to break Cooper pairs, either by direct absorption or through an antenna, excess quasiparticles are created. Due to the change in Cooper pairs and quasiparticle densities, the resonator shifts to a lower resonance frequency while the internal losses increase. We can measure this change using a homodyne microwave readout scheme. This thesis describes my work of the past four to five years on hybrid lumped element kinetic inductance detectors based on high resistivity disordered superconductors. The thesis can be divided into four parts: A theoretical and experimental background, the energy resolution of hybrid lumped element KIDs, improving the quantum efficiency of KIDs based on high resistivity superconductors with antireflection coatings and optical stacks, and reducing the pixel pitch of KIDs with parallel plate capacitors...