Accurate experimental and theoretical comparisons between superconductor-insulator-superconductor mixers showing weak and strong quantum effects

Journal Article · Fri Apr 15 04:00:00 EDT 1988 · J. Appl. Phys.; (United States)

DOI:https://doi.org/10.1063/1.341026· OSTI ID:5276562

McGrath, W R; Richards, P L; Face, D W; Prober, D E; Lloyd, F L

We have made a systematic study of the gain and noise in superconductor-insulator-superconductor mixers employing Ta based, Nb based, and Pb-alloy based tunnel junctions. These junctions displayed both weak and strong quantum effects at a signal frequency of 33 GHz. The effects of energy gap sharpness and subgap current were investigated and are quantitatively related to mixer performance. Detailed comparisons are made of the mixing results with the predictions of a three-port model approximation to the Tucker theory. We have measured mixer performance with a novel test apparatus which is accurate enough to allow for the first quantitative tests of theoretical noise predictions. We find that the three-port model of the Tucker theory underestimates the mixer noise temperature by a factor of about 2 for all of our mixers. In addition, predicted values of available mixer gain are in reasonable agreement with experiment when quantum effects are weak. However, as quantum effects become strong, the predicted available gain diverges to infinity, which is in sharp contrast to the experimental results. Predictions of coupled gain do not always show such divergences.

• Research Organization: Department of Physics, University of California, Berkeley, California 94720
• OSTI ID: 5276562
• Journal Information: J. Appl. Phys.; (United States), Journal Name: J. Appl. Phys.; (United States) Vol. 63:8; ISSN JAPIA
• Country of Publication: United States
• Language: English

Related Subjects

420201* -- Engineering-- Cryogenic Equipment & Devices
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AMPLIFICATION
DETECTION
GAIN
MEASURING INSTRUMENTS
MIXERS
NOISE
OPTIMIZATION
RADIATION DETECTION
RADIATION DETECTORS
SUPERCONDUCTING DEVICES