Materials loss measurements using superconducting microwave resonators

The performance of superconducting circuits for quantum computing is limited by materials losses in general, and two-level system (TLS) losses in particular, 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 loss performance and studying loss mechanisms such as TLS loss, 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 loss tangents, summarizing techniques that have been evolving for over two decades. Results from measurements of a 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.

• Quantum Computing