## An argon ion beam milling process for native $\text{AlO}_\text{x}$ layers enabling coherent superconducting contacts

16 Jun 2017  ·  Grünhaupt Lukas, von Lüpke Uwe, Gusenkova Daria, Skacel Sebastian T., Maleeva Nataliya, Schlör Steffen, Bilmes Alexander, Rotzinger Hannes, Ustinov Alexey V., Weides Martin, Pop Ioan M. ·

We present an argon ion beam milling process to remove the native oxide layer forming on aluminum thin films due to their exposure to atmosphere in between lithographic steps. Our cleaning process is readily integrable with conventional fabrication of Josephson junction quantum circuits... From measurements of the internal quality factors of superconducting microwave resonators with and without contacts, we place an upper bound on the residual resistance of an ion beam milled contact of 50$\,\mathrm{m}\Omega \cdot \mu \mathrm{m}^2$ at a frequency of 4.5 GHz. Resonators for which only $6\%$ of the total foot-print was exposed to the ion beam milling, in areas of low electric and high magnetic field, showed quality factors above $10^6$ in the single photon regime, and no degradation compared to single layer samples. We believe these results will enable the development of increasingly complex superconducting circuits for quantum information processing. read more

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Quantum Physics Superconductivity