Understanding the Saturation Power of Josephson Parametric Amplifiers Made from SQUID Arrays

TLDR: In this paper, a Josephson-junction array was used to increase the saturation power of a JPA, rather than using a single-JPA amplifier, and the array was modeled as a nonlinear $L\phantom{\rule{0}{0ex}}C$ resonator.

Abstract: Josephson parametric amplifiers (JPAs) are key devices in superconducting quantum circuits, as they ultimately dictate quantum efficiency and speed of measurement, but they still suffer from low saturation power. This work shows that a JPA's saturation power can be increased by using a Josephson-junction array, rather than a single-junction amplifier. Modeling such an array as a nonlinear $L\phantom{\rule{0}{0ex}}C$ resonator reproduces the observed amplification and saturation effects very well. This use of arrays to fight low power saturation is easy to implement, and can be directly combined with impedance-engineered environments to enhance dynamic range even more.