Two tone response of radiofrequency signals using the voltage output of a Superconducting Quantum Interference Filter

TL;DR

This paper demonstrates how superconducting quantum interference filters (SQIFs) can be used as nonlinear mixers for radiofrequency signals, exploiting their voltage response to weak electromagnetic fields to detect mixed signals at various frequencies.

Contribution

The study introduces a novel application of SQIFs as nonlinear RF mixers capable of operating from DC to GHz frequencies, utilizing their unique voltage dip shape for quadratic mixing.

Findings

Successfully mixed RF signals at frequencies below the Josephson frequency.

Detected mixing signals at difference frequencies, e.g., f_1 - f_2.

Potential for SQIFs to serve as broadband nonlinear mixing devices.

Abstract

In the presence of weak time harmonic electromagnetic fields, Superconducting Quantum Interference Filters (SQIFs) show the typical behavior of non linear mixers. The SQIFs are manufactured from high-T_c grain boundary Josephson junctions and operated in active microcooler. The dependence of dc voltage output V_dc vs. static external magnetic field B is non-periodic and consists of a well pronounced unique dip at zero field, with marginal side modulations at higher fields. We have successfully exploited the parabolic shape of the voltage dip around B=0 to mix quadratically two external time harmonic rf-signals, at frequencies f_1 and f_2 below the Josephson frequency f_J, and detect the corresponding mixing signal at f_1-f_2. When the mixing takes place on the SQIF current-voltage characteristics the component at 2f_2 - f_1 is present. The experiments suggest potential applications of a SQIF as a non-linear mixing device, capable to operate at frequencies from dc to few GHz with a large dynamic range.