Optical Direct Write of Dolan--Niemeyer-Bridge Junctions for Transmon Qubits

Abstract

We characterize highly coherent transmon qubits fabricated with a direct-write photolithography system. Multi-layer evaporation and oxidation allows us to change the critical current density by reducing the effective tunneling area and increasing the barrier thickness. Surface treatments before resist application and again before evaporation result in high coherence devices. With optimized surface treatments we achieve energy relaxation $T_1$ times in excess of $80\ \mu$s for three dimensional transmon qubits with Josephson junction lithographic areas of 2 $\mu\mathrm{m}^2$.