Quadratic Mixing of Radio Frequency Signals using Superconducting Quantum Interference Filters

TL;DR

This paper demonstrates quadratic mixing of weak RF signals using superconducting quantum interference filters made from high-temperature grain boundary Josephson junctions, with results matching a simple analytical model.

Contribution

It introduces a novel method for quadratic RF signal mixing using SQIFs operated in active microcoolers, expanding their application scope.

Findings

Successful quadratic mixing of RF signals below Josephson frequency

Mixing occurs without magnetic shielding

Experimental results align with the analytical model

Abstract

The authors demonstrate quadratic mixing of weak time harmonic electromagnetic fields applied to Superconducting Quantum Interference Filters, manufactured from high-$T_{\mathrm{c}}$ grain boundary Josephson junctions and operated in active microcooler. The authors use the parabolic shape of the dip in the dc-voltage output around B=0 to mix \emph{quadratically} two external rf-signals, at frequencies $f_{\mathrm{1}}$ and $f_{\mathrm{2}}$ well below the Josephson frequency $f_{\mathrm{J}}$, and detect the corresponding mixing signal at $| {f_{1}-f_{2}}| $. Quadratic mixing takes also place when the SQIF is operated without magnetic shield. The experimental results are well described by a simple analytical model based on the adiabatic approximation.