# Loss and Saturation in Superconducting Travelling-Wave Parametric Amplifiers

## TL;DR

This paper introduces a coupled-mode analysis framework for superconducting travelling-wave parametric amplifiers that accounts for loss, explaining experimental observations and guiding design improvements.

## Contribution

It presents a novel analytical model based on the full Telegrapher's equations to understand loss, gain saturation, and amplifier concatenation effects in superconducting amplifiers.

## Key findings

- Loss mechanisms explained by the model
- Concatenation enhances gain as predicted
- Signal gain saturation behavior clarified

## Abstract

We have developed a coupled-mode analysis framework for superconducting travelling-wave parametric amplifiers using the full Telegrapher's equations to incorporate loss-related behaviour. Our model provides an explanation of previous experimental observations regarding loss in amplifiers, advantages of concatenating amplifiers to achieve high gains, and signal gain saturation. This work can be used to guide the design of amplifiers in terms of the choice of material systems, transmission line geometry, operating conditions, and pump strength.