Correlating reductions in TLS density in Josephson junctions with fabrication methods and microstructure

Materials defects in Josephson junctions (JJs), often referred to as two-level systems (TLS), interact with qubits via electrical dipole coupling and reduce coherence and device reliability. Understanding their origin requires the characterization of large numbers of defects and correlating their presence with device fabrication methods. In this talk, we introduce an autonomous measurement and analysis pipeline for detecting TLS signatures in flux-tunable superconducting quantum circuits. The high throughput of our approach enables systematic exploration of the effects of fabrication on TLS density. We test this approach using JJ array resonators and detect hundreds of individual TLS across five fabrication treatments. Among these treatments, only the resonators with thicker electrodes show a reduction in TLS density. Structural analysis reveals that these samples also possess larger lateral grain sizes, suggesting that engineering junction microstructure could play a key role in reducing the prevalence of TLS.