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

TL;DR

This paper demonstrates a novel direct-write photolithography method for fabricating highly coherent transmon qubits with improved energy relaxation times exceeding 80 microseconds, using optimized surface treatments and multilayer evaporation techniques.

Contribution

It introduces a direct-write fabrication process for transmon qubits that achieves high coherence by optimizing surface treatments and multilayer evaporation to control junction properties.

Findings

Achieved $T_1$ times over 80 microseconds in transmon qubits.

Controlled critical current density through multilayer evaporation.

Surface treatments significantly improve qubit coherence.

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 $\mu\mathrm{m}^2$.