Understanding Materials-Level Sources of Performance Variations in Superconducting Qubits

Advances in our understanding of materials have played a crucial role in driving recent increases in achievable coherence times and gate fidelities in superconducting transmon qubits. This includes identifying defects, impurities, interfaces, and surfaces that can potentially introduce two-level systems (TLS) or non-TLS dissipation as well as implementing new strategies to mitigate the deleterious effects introduced by these sources of quantum decoherence. As part of the Superconducting Materials and Systems (SQMS) center, a DOE National Quantum Information Science Research Center, we have conducted a comprehensive and coordinated blind study with qubit chips of known performance variations probed across multiple institutions, including Ames Lab, Northwestern, and Fermilab, in an effort that brings together over 40 researchers in the materials science and superconducting materials domains. These qubits have been interrogated with various unique non-destructive and destructive characterization techniques to pinpoint the underlying materials-level sources of device-to-device performance variation giving rise to decoherence. Preliminary findings suggest a correlation between variations in magnetic flux penetration, surface oxide quantities, and sidewall geometries with microwave loss across different devices. These insights provide a pathway to not only reduce performance variations but also to fabricate devices with performance metrics beyond state-of-the-art values.