Contacting Josephson Junctions via Airbridges in Superconducting Circuits

Abstract

Superconducting circuit devices require electrical interconnects between different circuit elements on the chip, for which conventional device architectures use a combination of two structural elements: \textit{airbridges} to connect non-adjacent elements in the base layer, and \textit{bandages} to connect the electrodes forming the Josephson junctions to the base layer. Bandages introduce unwanted parasitic material interfaces and increase the manufacturing complexity. Here, we overcome the limitations imposed by \emph{bandages} by establishing \textit{all} electrical interconnects with airbridges of varying size fabricated in a single step. The airbridges show a high yield and mechanical stability over a wide range of sizes from $0.5\,μ\mathrm{m}$ to $4\,μ\mathrm{m}$ in width and from $5\,μ\mathrm{m}$ to $40\,μ\mathrm{m}$ in length, and show low loss when integrated in coplanar waveguide resonators and transmon qubits. Measured relaxation times up to more than $250\,μ\mathrm{s}$ in standard transmon geometries show that the process achieves high coherence while substantially easing and accelerating device fabrication.