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physica status solidi (a)

Harmonics mixing in superconducting point contacts

A. I. Akimenko, В. С. Соловьев, I. K. Yanson

Published Jan 16, 1976• 0 citations
Publisher

Abstract

The experimental results are decribed of mixing the ninth harmonic of an rf signal of the 3 cm range with a 4 mm range signal. Such mixers are found to have a maximum sensitivity of ≈︁ 10−14 W/Hz, transformation losses of 45 to 50 dB, and dynamic range of 20 to 30 dB.
DOI
10.1002/pssa.2210330103

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A millimeter band mixer employing Nb--Nb superconducting point contacts at 4.2/sup 0/K with an external heterodyne was investigated experimentally. It is shown that the mixing model needs to be somewhat more complex. The distortions of the IF signal, the effect of the IF currents on the I-V characteristic of the contacts, the dynamic characteristics, and cases of deviation from the mixing model are examined. The best contacts have an NEP approximately 0.5 x 10/sup -15/ W/Hz and conversion losses of approximately 30 db.
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The Josephson frequency conversion in the millimeter and submillimeter wave region is studied with superconducting Nb-Nb point contact junctions at 4.2 K, using the contact both as the local oscillator and the mixer with intermediate frequencies of 0.1 and 9.2 GHz. Frequency conversion signals are only detected in the latter case with a microwave receiver at 9.2 GHz in a range of Josephson frequencies between 145 and 1 600 GHz. The experiments with intermediate frequency fi of 0.1 GHz indicate for this small value of f i that the observed signals are not related to frequency conversion but noise effects. An analysis of the frequency conversion mechanism in a Josephson junction operated as an oscillator-mixer is proposed which includes the noise effects and also the feedback effects induced in a junction driven by a constant current source. We have then investigated the noise properties up to 450 GHz of superconducting point-contacts using the junction as an oscillator-mixer where the Josephson current is mixed with harmonics of an externally applied signal. The emitted intermediate frequency is detected at 9.2 GHz and its linewidth is measured. In the very high frequency range the dc quasiparticle current dominates in a Josephson weak-link and we compare the corresponding theoretical linewidth calculated by Scalapino with our experimental results.
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