Josephson junction metal encapsulation and its effect on junction and superconducting qubit performance

Materials design and fabrication play a pivotal role towards enhancing the performance of superconducting qubits¹. For instance, by fabricating the shunting capacitor of a transmon qubit with materials that produce less lossy oxides, like Ta, qubit T₁ lifetimes can exceed a millisecond². Whether improvements in qubit performance can result from materials engineering of the Josephson junction remains an open question. In this talk, we will present on the metal encapsulation of Josephson junctions using Ti and Ta and discuss its effects on junction and superconducting qubit performance.

¹I. Siddiqi et al. Nat. Rev. Mater. 6, 875–891 (2021)

²M. Bland et al. arXiv:2503.14798