Characterization of Asymmetric Gap-Engineered Josephson Junctions and 3D Transmon Qubits

Abstract

We have fabricated and characterized asymmetric gap-engineered junctions and transmon devices. To create Josephson junctions with asymmetric gaps, Ti was used to proximitize and lower the superconducting gap of the Al counter-electrode. DC IV measurements of these small, proximitized Josephson junctions show a reduced gap and larger excess current for voltage biases below the superconducting gap when compared to standard Al/AlO/x/Al junctions. The energy relaxation time constant for an Al/AlO/x/Al/Ti 3D transmon was T1= 1s, over two orders of magnitude shorter than the measured T1 = 134s of a standard Al/AlO/x/Al 3D transmon. Intentionally adding disorder between the Al and Ti layers reduces the proximity effect and subgap current while increasing the relaxation time to T1 = 32s.