Interplay between critical current density and non-linearity in microwave kinetic inductance detectors

by Francesco Valenti (KIT)

Wednesday 18 Jul 2018, 14:00 → 15:00 Europe/Rome

Sala Touschek (Dipartimento di Fisica - Ed. G.Marconi)

Microwave kinetic inductance detectors (MKIDs) are thin film superconducting resonators. Incident pair-breaking radiation increases their kinetic inductance and lowers their resonance frequency. The responsivity of MKIDS scales with their kinetic inductance fraction α. However, this lowers the supercurrent density and reduces the maximum number of readout photons before bifurcation due to self-Kerr non-linearity, resulting in an increased noise equivalent power (NEP). We quantify this interplay and predict NEP values based on microscopic parameters. We sketch the quasiparticle dynamics between resonators and ground plane and show that the phonon trapping effect of the latter reduces the NEP.