Signal-to-pump back-action and self-oscillation in Double-Pump Josephson Parametric Amplifier

TL;DR

This paper develops a theoretical model for a double-pump Josephson parametric amplifier, analyzing back-action effects, self-oscillation, and the conditions for amplification and coherent emission, with implications for quantum measurements.

Contribution

It introduces a mean-field approach to account for back-action in a double-pump Josephson amplifier, revealing hysteresis and resonance shifts due to multi-wave mixing.

Findings

Back-action causes hysteresis and modifies resonance conditions.

Self-oscillation threshold coincides with bifurcation point.

System can operate near quantum-limited measurement regimes.

Abstract

We present the theory of a Josephson parametric amplifier employing two pump sources. Our calculations are based on Input-Output Theory, and can easily be generalized to any coupled system involving parametric interactions. We analyze the operation of the device, taking into account the feedback introduced by the reaction of the signal and noise on the pump power, and in this framework, compute the response functions of interest - signal and idler gains, internal gain of the amplifier, and self-oscillation signal amplitude. To account for this back-action between signal and pump, we adopt a mean-field approach and self-consistently explore the boundary between amplification and self-oscillation. The coincidence of bifurcation and self-oscillation thresholds reveals that the origin of coherent emission of the amplifier lies in the multi-wave mixing of the noise components. Incorporation of the back-action leads the system to exhibit hysteresis, dependent on parameters like temperature and detuning from resonance. Our analysis also shows that the resonance condition itself changes in the presence of back-action and this can be understood in terms of the change in plasma frequency of the junction. The potential of the double pump amplifier for quantum-limited measurements and as a squeezer is also discussed.