Aluminum air bridges for superconducting quantum devices realized using a single step electron-beam lithography process

Abstract

In superconducting quantum devices, air bridges enable increased circuit complexity and density as well as mitigate the risk of microwave loss arising from mode mixing. We implement aluminum air bridges using a simple process based on single-step electron-beam gradient exposure. The resulting bridges have sizes ranging from $20~\mu m$ to $100~\mu m$, with a yield exceeding $99~\%$ for lengths up to $36~\mu m$. When used to connect ground planes in coplanar waveguide resonators, the induced loss contributed to the system is negligible, corresponding to a reduction of the quality factor exceeding $1.0\times10^8$ per bridge. The bridge process is compatible with Josephson junctions and allows for the simultaneous creation of low loss bandages between superconducting layers.