Fabrication and characterization of low loss niobium airbridges for superconducting quantum circuits

Abstract

Airbridges are extensively employed in superconducting quantum circuits to suppress parasitic slotline modes in coplanar waveguide and minimize crosstalk between control lines. Here, we introduce a fabrication technique for airbridges, leveraging niobium as the bridge layer and aluminum as the sacrificial layer to preclude the introduction of lossy dielectrics or residues upon release. Additionally, we utilize a triangular evaporation method to significantly bolster the structural integrity of the airbridges. Our experimental evaluation, focused on resonators equipped with these airbridges, reveals that the resultant additional loss per bridge is minimal, quantified at (5.0±2.8)×10−9 in the single-photon regime and (6.3±0.9)×10−9 at high drive powers. This advancement underscores the potential of niobium airbridges in facilitating the development of large-scale and high-performance superconducting quantum circuits.