Optimizing Josephson-Ring-Modulator-based Josephson Parametric Amplifiers via full Hamiltonian control

TL;DR

This paper analyzes the nonlinearities in Josephson Parametric Amplifiers, especially those based on Josephson Ring Modulators, and proposes circuit tuning strategies to significantly enhance their saturation power, improving quantum sensing capabilities.

Contribution

It identifies the nonlinearities limiting JPA saturation power and introduces a systematic optimization method for circuit parameters to enhance performance.

Findings

Saturation power limited by high-order nonlinearities, not pump depletion.

Tuning inductors can improve saturation power by approximately 15 dB.

Methods applicable to a broad range of cavity-based JPAs.

Abstract

Josephson Parametric Amplifiers (JPA) are nonlinear devices that are used for quantum sensing and qubit readout in the microwave regime. While JPAs regularly operate in the quantum limit, their gain saturates for very small (few photons) input power. In a previous work, we showed that the saturation power of JPAs is not limited by pump depletion, but instead by the high-order nonlinearity of Josephson junctions, the nonlinear circuit elements that enable amplification in JPAs. Here, we present a systematic study of the nonlinearities in JPAs, we show which nonlinearities limit the saturation power, and present a strategy for optimizing the circuit parameters for achieving the best possible JPA. For concreteness, we focus on JPAs that are constructed around a Josephson Ring Modulator (JRM). We show that by tuning the external and shunt inductors, we should be able to take the best experimentally available JPAs and improve their saturation power by $\sim 15$ dB. Finally, we argue that our methods and qualitative results are applicable to a broad range of cavity based JPAs.