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International Conference on Submillimeter Waves and Their Applications

Evidence for 1.6 mm Wavelength Parametric Amplification in a Josephson Junction Microwave Source

Mogens T. Levinsen, B. T. Ulrich

Published Jun 1, 1974• 0 citations
Publisher

Abstract

A Josephson junction 1.6 mm wavelength microwave source has been used to demonstrate the parametric amplification by reflection necessary to maintain parametric oscillations at 1.6 mm wavelength. A perturbation calculation based on the resistively and capacitively shunted Josephson junction model gives a negative effective microwave resistance for a junction biased at voltages higher than the voltage for a cavity induced step. The parametric oscillation was observed at voltages consistent with the region in which negative resistance was calculated.

DOI
10.1109/icswa.1974.9333712

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A Josephson junction 1.6 mm wavelength microwave source has been used to demonstrate the parametric amplification by reflection necessary to maintain parametric oscillations at 1.6 mm wavelength. A perturbation calculation based on the resistively and capacitively shunted Josephson junction model gives a negative effective microwave resistance for a junction biased at voltages higher than the voltage for a cavity induced step. The parametric oscillation was observed at voltages consistent with the region in which negative resistance was calculated.
Our observation of 1−mm wavelength radiation generated in a cavity containing a Josephson junction provides evidence for a negative effective microwave resistance in the Josephson junction, and for parametric amplification in the reflection mode by the Josephson junction. These parametric oscillations were observed at wavelengths corresponding to cavity resonances between 1.1− and 2−mm wavelength. The frequency of the emitted radiation differed from the frequency given by ν=2eV/h, and thus the radiation was not simply from the ac Josephson effect. We develop a theory that predicts a negative microwave resistance at junction bias voltages just below a cavity−induced step for resistively shunted junction, and just above the cavity−induced step for a junction with sufficient shunt capacitance. Our observations are consistent with the theory.
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.
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.
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)
Conventional negative resistance effects can be generated with a Josephson junction quite similar to that obtained with Varactor diodes, with the additional advantage that the internal, self-generated oscillations serve as a pump, i. e., only a dc source is needed instead of a high frequency pump source. However, another negative resistance effect typical for a Josephson junction is possible as has been predicted recently for the current controlled, highly damped junction model. The effect has recently been demonstrated experimentally at 9 GHz. Characteristically, the pump (Josephson) frequency is smaller than the frequency of the amplified signal and the pump mechanism is effective over a broad range of frequencies in contrast to the conventional parametric negative resistance effect where the pump frequency exceeds that of the signal and idler and where the frequency of operation is limited to a narrow range. The broad-band feature renders the amplifier operation uncritical to tuning and bias voltage fluctuations. The fact that the junction is the element of lowest impedance in the circuit alleviates to a degree the matching problem generally encountered with Josephson contacts. An assessment of the competitiveness of this effect in microwave technology is given.
We consider a current biased, resistively shunted josephson junction irradiated at two frequencies. The perturbation technique introduced by Aslamasov and Larkin is used in the calculations. Both signals are treated as perturbations. The second order calculation yields the size of the mixing steps atV_{\pm}=h(\omega_{1}\pm\omega_{2})/2e. As in the case of a single frequency we show that subharmonic mixing steps are absent. The amplitude of the voltage oscillation at the difference and sum frequencies is shown to be non-zero at all voltages. We calculate the microwave resistance for one frequency ω2to third order in the perturbation. There are negative resistance regions nearV\pm(as well as nearV_{2}= h\omega_{2}/2e). Near V, the negative resistance region appears for bias voltage V just aboveV_{-}, while near V the region appears for V just belowV_{+}. This means that when an incident frequency mixes with a cavity mode the mixing step atV_{-}will be inverted compared to the cavity step itself.