SLUG Microwave Amplifier: Theory

TL;DR

This paper introduces a new microwave amplifier scheme using the superconducting SLUG device, capable of near-quantum-limited noise performance with significant gain and bandwidth.

Contribution

It presents a comprehensive theoretical analysis and optimization strategies for the SLUG amplifier, including its scattering matrix, gain, noise, and decoupling techniques.

Findings

Achieves near-quantum-limited noise performance at 5-10 GHz

Provides approximately 15 dB gain and 1 GHz bandwidth

Offers strategies for minimizing mode coupling and optimizing gain

Abstract

We describe a novel scheme for low-noise phase-insensitive linear amplification at microwave frequencies based on the Superconducting Low-inductance Undulatory Galvanometer (SLUG). Direct integration of the junction equations of motion provides access to the full scattering matrix of the SLUG. We discuss the optimization of SLUG amplifiers and calculate amplifier gain and noise temperature in both the thermal and quantum regimes. Loading of the SLUG element by the finite input admittance is taken into account, and strategies for decoupling the SLUG from the higher-order modes of the input circuit are discussed. The microwave SLUG amplifier is expected to achieve noise performance approaching the standard quantum limit in the frequency range from 5-10 GHz, with gain around 15 dB for a single-stage device and instantaneous bandwidths of order 1 GHz.