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

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
$\mathrm{_{x}}$
/Al junctions. The energy relaxation time constant for an Al/AlO
$\mathrm{_{x}}$
/Al/Ti 3D transmon was
$T_{1}= 1\ \mu$
s, over two orders of magnitude shorter than the measured
$T_{1} = 134\ \mu$
s of a standard Al/AlO
$\mathrm{_{x}}$
/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
$T_{1} = 32\ \mu$
s.