Forty five nanoseconds superconducting delay lines

The authors report on the design, simulation, fabrication, and measurement of very long superconducting coplanar waveguide delay lines on 3-in-diameter LaAlO/sub 3/ substrates. Variations of the design involving the addition of a ground plane on the backside of the substrate and for the use of gold wire-bond bridges to electrically connect the in-plane ground planes were investigated. A delay of 45 ns was measured for a line length of 4.3 m. The best response was obtained with wire-bond connections and no backside ground plane. A resonance-free insertion loss of less than 0.01 dB/ns was obtained with a 1.7-GHz bandwidth for NbN at 4.2 K. This is to be compared with a loss of 0.1 dB/ns for a 50-ns 0.141-in OD. (outer diameter) copper coaxial delay line that weighs 1.5 lb and 0.02 dB/ns for a 60-ns 1-in OD copper coaxial delay line that weighs 45 lb.>