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Niobium air bridges as low-loss components for superconducting quantum hardware

N. Bruckmoser1,2,*, L. Koch1,2,†, I. Tsitsilin1,2, M. Grammer1,2, D. Bunch1,2, L. Richard1,2, J. Schirk1,2, F. Wallner1,2, J. Feigl1,2 et al.

C.M.F. Schneider1,2, S. Geprägs2, V.P. Bader2, M. Althammer1,2, L. Södergren1,2, and S. Filipp1,2,3

  • *Contact author: Niklas.Bruckmoser@wmi.badw.de
  • †Contact author: Leon.Koch@wmi.badw.de
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Phys. Rev. Applied 25, 024007 – Published 3 February, 2026

DOI: https://doi.org/10.1103/smlq-r7x6

Abstract

Scaling up superconducting quantum processors necessitates the use of a high routing density for readout and control lines, relying on low-loss interconnects to maintain design flexibility and device performance. We propose and demonstrate a universal subtractive fabrication process for air bridges based on an aluminum hard mask and niobium as the superconducting film. Using this technology, we fabricate superconducting coplanar waveguide resonators incorporating several niobium air bridges in and across their center conductors. Through rigorous cleaning methods, we achieve mean internal quality factors in the single-photon limit exceeding Qint=8.2×106. Notably, the loss per air bridge remains below the detection threshold of the resonators. Due to the larger superconducting energy gap of niobium, compared with conventional aluminum air bridges, our approach enables stable performance at elevated temperatures and magnetic fields, which we experimentally confirm in temperatures up to 3.9 K and in a magnetic field of up to 1.60 T. Additionally, we utilize air bridges to realize low-loss vacuum-gap capacitors and demonstrate their successful integration in transmon qubits by achieving median qubit lifetimes of T1=51.6μs.

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synopsis

Building Better Bridges on Quantum Chips

Published 3 February, 2026

Fabricating some structures using niobium instead of aluminum could lead to more resilient superconducting quantum computers.

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Phys. Rev. Applied 25, 024007– Published 3 February, 2026
  • Received 10 June 2025
  • Revised 19 November 2025
  • Accepted 9 December 2025
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