Tunable microwave impedance matching to a high impedance source using a Josephson metamaterial

We report the efficient coupling of a 50 ? microwave circuit to a high impedance conductor. We use an impedance transformer consisting of a ? / 4 co-planar resonator whose inner conductor contains an array of superconducting quantum interference devices (SQUIDs), providing it with a tunable lineic inductance L ~ 80 ? 0, resulting in a characteristic impedance Z C ~ 1 k ?. The impedance matching efficiency is characterized by measuring the shot noise power emitted by a dc biased tunnel junction connected to the resonator. We demonstrate matching to impedances in the 15 to 35 k ? range with bandwidths above 100 MHz around a resonant frequency tunable between 4 and 6 GHz. © 2013 AIP Publishing LLC.