Investigating pump harmonics generation in a SNAIL-based Traveling Wave Parametric Amplifier

TL;DR

This paper experimentally investigates harmonic generation in a SNAIL-based TWPA, analyzing how fabrication imperfections affect nonlinear processes and amplification performance in broadband quantum-limited devices.

Contribution

It provides new insights into the impact of Josephson junction imperfections on harmonic generation and gain in SNAIL-based TWPAs through combined experiments and simulations.

Findings

Harmonics are influenced by junction fabrication imperfections.

Experimental and simulation results show the effect on gain behavior.

Second and third harmonics are actively generated during operation.

Abstract

Traveling Wave Parametric Amplifiers (TWPAs) are extensively employed in experiments involving weak microwave signals for their highly desirable quantum-limited and broadband characteristics. However, TWPAs' broadband nature comes with the disadvantage of admitting the activation of spurious nonlinear processes, such as harmonics generation, that can potentially degrade amplification performance. Here we experimentally investigate a Josephson TWPA device with SNAIL (Superconducting Nonlinear Asymmetric Inductive Element)-based unit cells focusing on the amplification behaviour along with the generation of second and third harmonics of the pump. By comparing experimental results with transient numerical simulations, we demonstrate the influence of Josephson junctions' fabrication imperfections on the occurrence of harmonics and on the gain behaviour.