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Journal of Applied Physics

Parametric amplification on rf-induced steps in a Josephson tunnel junction

O. H. Soerensen, N. F. Pedersen, J. Mygind, Bjørn Dueholm

Published Apr 1, 1979• 6 citations
Publisher

Abstract

Parametric effects including amplification in a singly degenerate mode have been observed in Josephson tunnel junctions at dc bias points on rf-induced steps. Net gain at 9 GHz was achieved with a bias on the fundamental 18-GHz step and subharmonic self-oscillations were seen on 18 and 70-GHz rf-induced steps even at voltages approaching the energy gap. A qualitative explanation of the results is presented.

DOI
10.1063/1.326184

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Physical review. B, Condensed matter•May 1, 1991•31 citations
Parametric effects including amplification in a singly degenerate mode have been observed in Josephson tunnel junctions at dc bias points on rf-induced steps. Net gain at 9 GHz was achieved with a bias on the fundamental 18-GHz step and subharmonic self-oscillations were seen on 18 and 70-GHz rf-induced steps even at voltages approaching the energy gap. A qualitative explanation of the results is presented.
We have observed doubly degenerate parametric amplification and oscillation at 36 GHz from a single point-contact Josephson junction. The experimental results agree qualitatively with theoretical calculations based on the resistively shunted junction model. The estimated noise temperature of an amplifier with 11 dB net gain is consistent with zero, but has an upper limit of 50 K. Attempts to observe parametric amplification in the singly degenerate mode with a pump frequency of 72 GHz were not successful.
We have observed doubly degenerate parametric amplification and oscillation at 36 GHz from a single point contact Josephson junction. The experimental results agree qualitatively with theoretical calculations based on the resistively shunted junction model. The estimated noise temperature of an amplifier with 11 dB net gain is consistent with zero, but has an upper limit of 50 K. Attempts to observe parametric amplification in the singly degenerate mode with a pump frequency of 72 GHz were not successful. (Author)
Doubly degenerate parametric amplification and oscillation at 36 GHz was observed from a single point contact Josephson junction. The experimental results agree qualitatively with theoretical calculations based on the resistively shunted junction model. The estimated noise temperature of an amplifier with 11 dB net gain is consistent with zero, but has an upper limit of 50 K. Attempts to observe parametric amplification in the singly degenerate mode with a pump frequency of 72 GHz were not successful.
An equally spaced series of very large and nearly constant-voltage self-induced singularities has been observed in the dc I-V characteristics of a small Josephson tunnel junction strongly coupled to a resonant section of a superconducting transmission line. The system allows extremely high values of the coupling parameter. The current steps are due to subharmonic parametric excitation of the fundamental mode of the resonator loaded by the junction admittance. Using an applied magnetic field to vary the coupling parameter, we traced out half-integer steps as well as the mode steps known from more weakly coupled systems. Based on a single-resonator model, we explain the exceptional size of the steps by the large content of higher harmonics of the Josephson oscillation sustained by the multiple modes of the resonator. The parameters of the junction and the loaded resonator---measured in situ by using the junction as detector---form a consistent set. The dominant system loss originates in the junction but cannot be ascribed to a relevant conductance.