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

Abstract

We report the efficient coupling of a $50\hat{I}\text{c◯}$ microwave circuit to a high impedance conductor. We use an impedance transformer consisting of a $\hat{I}»/4$ co-planar resonator whose inner conductor contains an array of superconducting quantum interference devices (SQUIDs), providing the resonator with a large and tunable lineic inductance $\mathcal{L}\sim 80\hat{I}{¼}_0$, resulting in a large characteristic impedance $Z_C\sim 1\mathrm{k}\hat{I}\text{c◯}$. The impedance matching efficiency is characterized by measuring the shot noise power emitted by a dc biased high resistance tunnel junction connected to the resonator. We demonstrate matching to impedances in the $15$ to $35\mathrm{k}\hat{I}\text{c◯}$ range with bandwidths above $100\mathrm{MHz}$ around a resonant frequency tunable in the $4$ to $6\mathrm{GHz}$ range.

Published in Applied Physics Letters