Two tone response of radiofrequency signals using the voltage output of a Superconducting Quantum Interference Filter
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-Tc grain boundary Josephson junctions and operated in active microcooler. The dependence of dc voltage output Vdc 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 f1 and f2 below the Josephson frequency fJ, and detect the corresponding mixing signal at f1-f2. When the mixing takes place on the SQIF current-voltage characteristics the component at 2f2 - f1 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.
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