# Characterization of low loss microstrip resonators as a building block for circuit QED in a 3D waveguide

## TL;DR

This paper reports on the microwave characterization of aluminum and niobium microstrip resonators within a 3D waveguide, achieving high quality factors and demonstrating their potential as building blocks for circuit QED architectures.

## Contribution

It introduces a wire-bond-free, well-controlled environment for testing resonators, and shows their suitability for integration with transmon qubits in 3D waveguide circuit QED.

## Key findings

- Internal quality factors up to one million at low temperature and power
- Good agreement with models predicting conductive and TLS losses
- Resonators serve as building blocks for 3D waveguide circuit QED

## Abstract

Here we present the microwave characterization of microstrip resonators made from aluminum and niobium inside a 3D microwave waveguide. In the low temperature, low power limit internal quality factors of up to one million were reached. We found a good agreement to models predicting conductive losses and losses to two level systems for increasing temperature. The setup presented here is appealing for testing materials and structures, as it is free of wire bonds and offers a well controlled microwave environment. In combination with transmon qubits, these resonators serve as a building block for a novel circuit QED architecture inside a rectangular waveguide.