Materials loss measurements using superconducting microwave resonators

TL;DR

This paper reviews methods for measuring materials losses in superconducting microwave resonators, which are crucial for improving quantum computing hardware by identifying low-loss materials and fabrication techniques.

Contribution

It provides a comprehensive overview of resonator design considerations, measurement techniques, and summarizes two decades of material loss data in superconducting circuits.

Findings

Various materials exhibit different loss characteristics at cryogenic temperatures.

Measurement techniques have evolved to improve accuracy in loss characterization.

Standardized reporting can enhance material comparison and selection.

Abstract

The performance of superconducting circuits for quantum computing is limited by materials losses. In particular, coherence times are typically bounded by two-level system (TLS) losses at single photon powers and millikelvin temperatures. The identification of low loss fabrication techniques, materials, and thin film dielectrics is critical to achieving scalable architectures for superconducting quantum computing. Superconducting microwave resonators provide a convenient qubit proxy for assessing performance and studying TLS loss and other mechanisms relevant to superconducting circuits such as non-equilibrium quasiparticles and magnetic flux vortices. In this review article, we provide an overview of considerations for designing accurate resonator experiments to characterize loss, including applicable types of loss, cryogenic setup, device design, and methods for extracting material and interface losses, summarizing techniques that have been evolving for over two decades. Results from measurements of a wide variety of materials and processes are also summarized. Lastly, we present recommendations for the reporting of loss data from superconducting microwave resonators to facilitate materials comparisons across the field.