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arXiv · 2608.07306

Flip-chip integrated superconducting qubits using electroplated bump bonds

Yen-An Shih·Rebecca Gharibaan·Barka Khan·Dhananjay Joshi·Siddharth Singh·Martijn F. S. Zwanenburg·Eugene Y. Huang·Nataliia Zhurbina·Figen Yilmaz·Lukas Johannes Splitthoff·Srijit Goswami·Christian Kraglund Andersen
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Abstract

Flip-chip integration offers a promising route toward scalable superconducting quantum processors and hybrid semiconductor-superconductor quantum devices. We develop a three-dimensional transmon architecture using electroplated indium in which the qubit electric field is shared nearly equally between two bump-bonded substrates while maintaining low participation at the indium-bump interface. The resulting geometry is well suited for future hybrid qubits, enabling the integration of distinct material platforms while minimizing sensitivity to bump-interface loss. Using this platform, we evaluate electroplated indium interconnects for superconducting quantum circuits. Flip-chip transmons incorporating electroplated indium bumps exhibit qubit quality factors around $10^6$. In addition, a systematic study of coplanar-waveguide resonators is used to identify losses associated with the electroplating process. In particular, we find that surface losses associated with the gold-layer, used to enable good electric contact with the indium, is likely the primary contributor to the qubit decay rate. These results demonstrate the compatibility of electroplated indium technology with high-coherence superconducting circuits and establish a promising platform for three-dimensional hybrid quantum integration.

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Yen-An Shih, Rebecca Gharibaan, Barka Khan, Dhananjay Joshi, Siddharth Singh, Martijn F. S. Zwanenburg, Eugene Y. Huang, Nataliia Zhurbina, Figen Yilmaz, Lukas Johannes Splitthoff, Srijit Goswami, Christian Kraglund Andersen. 2026-08-07. Flip-chip integrated superconducting qubits using electroplated bump bonds. https://arxiv.org/abs/2608.07306

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