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

## TL;DR

This paper reports on the fabrication and characterization of asymmetric gap-engineered Josephson junctions and 3D transmon qubits, revealing how material modifications affect their electrical properties and coherence times.

## Contribution

It introduces a method to engineer asymmetric gaps in Josephson junctions using Ti, and demonstrates how this impacts transmon qubit relaxation times.

## Key findings

- Proximitized junctions show reduced gaps and increased excess current.
- Standard Al/AlOx/Al transmon has T1 = 134 μs.
- Disorder reduces subgap current and increases T1 to 32 μs.

## 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/AlOx/Al junctions. The energy relaxation time constant for an Al/AlOx/Al/Ti 3D transmon was T1 = 1 {\mu}s, over two orders of magnitude shorter than the measured T1 = 134 {\mu}s of a standard Al/AlOx/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 = 32 {\mu}s.