Merged-Element Transmons: Design and Qubit Performance

We have demonstrated a novel type of superconducting transmon qubit in which Josephson junction has been engineered to act as its own parallel shunt capacitor. This merged-element (MET) potentially offers smaller footprint and simpler fabrication than conventional transmons. Because it concentrates the electromagnetic energy inside junction, reduces relative electric field participation from other interfaces. By combining micrometer-scale Al/AlOx/Al junctions with long oxidations processing, we produced functional devices $E_{J}$/$E_{C}$ low regime ($E_{J}$/$E_{C}$ $\lesssim$30). Cryogenic I-V measurements show sharp dI/dV structure sub-gap conduction. Qubit spectroscopy tunable versions small number avoided level crossings, suggesting presence two-level systems (TLS). observed mean T1 times typically range 10-90 microseconds, some annealed exhibiting > 100 microseconds over several hours. The results suggest that relaxation conventional, small-junction transmons is not limited by loss.