Investigation of Parasitic Two-Level Systems in Merged-Element Transmon Qubits

Studies junction and surface two-level systems in flux-tunable Al/AlO${}_x$/Al mergemons. The best design cohort reached mean $T_1$ values up to 130 μs ($Q\approx 3.3\times 10^6$). Geometry sweeps showed that exposed-surface participation can remain a major limitation even when junction energy participation exceeds 90%.

Key Results

• Mean $T_1$ up to 130 μs in flux-tunable devices
• Junction energy participation above 90% across the studied designs
• Strain and electric-field spectroscopy used to distinguish TLS classes
• Surface-loss mitigation remains necessary in the merged geometry

Links

• arXiv: 2509.22593

Zoo Links

• mergemon