Design of variable phase velocity kinetic inductance delay lines and their measured characteristics when fabricated by a simple Nb based process

Abstract

A simple design for superconducting kinetic inductance delay lines is presented. Delay lines were fabricated with a thin-film process involving only DC magnetron deposition and anodization of Nb. Phase-velocity measurements demonstrated wave slowing to less than 1/150 of the velocity of light in free space with associated impedances in the ohm range. Phase velocity changes on lines which were in physical proximity to long Josephson junctions and normal conducting lines were investigated. Variations larger than 10% of the equilibrium value were observed with junction-coupled lines under bias application. Locally heated lines exhibited changes exceeding a factor of two. Loss and phase velocity were determined as a function of bias conditions in both cases. Measured line loss was within expectations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>