Broadband architecture for galvanically accessible superconducting microwave resonators

TL;DR

This paper presents a broadband galvanic coupling method for superconducting microwave resonators using a large shunt capacitance, enabling DC biasing without degrading the resonator's quality.

Contribution

Introduction of a simple, broadband galvanic coupler for superconducting CPW resonators that maintains high quality factors during DC biasing.

Findings

Achieved voltage bias up to 80 V without quality degradation.

Demonstrated a resonator with MHz linewidths and Q~10^3.

No spurious resonances observed during biasing.

Abstract

In many hybrid quantum systems, a superconducting circuit is required that combines DC-control with a coplanar waveguide (CPW) microwave resonator. The strategy thus far for applying a DC voltage or current bias to microwave resonators has been to apply the bias through a symmetry point in such a way that it appears as an open circuit for certain frequencies. Here, we introduce a microwave coupler for superconducting CPW cavities in the form of a large shunt capacitance to ground. Such a coupler acts as a broadband mirror for microwaves while providing galvanic connection to the center conductor of the resonator. We demonstrate this approach with a two-port $\lambda/4$-transmission resonator with linewidths in the MHz regime ($Q\sim10^3$) that shows no spurious resonances and apply a voltage bias up to $80$ V without affecting the quality factor of the resonator. This resonator coupling architecture, which is simple to engineer, fabricate and analyse, could have many potential applications in experiments involving superconducting hybrid circuits.