Fabrication of Metal Air Bridges for Superconducting Circuits using Two-Photon Lithography

Extraneous high frequency chip modes parasitic to superconducting quantum circuits can result in decoherence when these modes are excited. To suppress these modes, superconducting air bridges are commonly used to electrically connect ground planes together when interrupted by transmission lines. In this talk, I will first begin by reviewing previous work on fabricating superconducting air bridges. I then will describe our work using two-photon photolithography to build a supporting 3D resist structure in conjunction with a liftoff process to create our air bridges. The resulting aluminum air bridges have a superconducting transition temperature of T_c = 1.08 K and exhibit good mechanical strength up to lengths of 100 μm. A measurable amount of microwave loss is observed when 35 air bridges were placed over a high-Q Ta quarter-wave coplanar waveguide resonator.