Introduction of a DC Bias into a High-Q Superconducting Microwave Cavity

TL;DR

This paper presents a method to apply dc bias to a high-Q superconducting microwave cavity with minimal impact on its performance, verified through measurements and simulations.

Contribution

It introduces a novel technique for integrating dc bias lines into superconducting cavities without significantly degrading their quality factor.

Findings

Quality factor degrades less than 1% at 4 K with dc bias

Measured S-matrix matches theoretical predictions

Method preserves cavity mode integrity during bias application

Abstract

We report a technique for applying a dc voltage or current bias to the center conductor of a high-quality factor superconducting microwave cavity without significantly disturbing selected cavity modes. This is accomplished by incorporating dc bias lines into the cavity at specific locations. The measured S-matrix parameters of the system are in good agreement with theoretical predictions and simulations. We find that at 4 K the quality factor of the cavity degrades by less than 1% under the application of a dc bias.