Contacting Josephson Junctions via Airbridges in Superconducting Circuits

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: airbridges to connect non-adjacent elements in the base layer, and 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 bandages by establishing 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 μm to 4 μm in width and from 5 μm to 40 μm in length, and show low loss when integrated in coplanar waveguide resonators and transmon qubits. Measured relaxation times up to more than 250 μs in standard transmon geometries show that the process achieves high coherence while substantially easing and accelerating device fabrication.