The coherence of state-of-the-art superconducting qubit devices is predominantly limited by two-level-system defects, found primarily at amorphous interface layers. Reducing microwave loss from these interfaces by proper surface treatments is key to push the device performance forward. Here, we study niobium resonators after removing the native oxides with a hydrofluoric acid etch. We investigate the reappearance of microwave losses introduced by surface oxides that grow after exposure to the ambient environment. We find that losses in quantum devices are reduced by an order of magnitude, with internal Qfactors reaching up to 7×10 6 in the single photon regime, when devices are exposed to ambient conditions for 16 min. Furthermore, we observe that Nb2O5 is the only surface oxide that grows significantly within the first 200 hours, following the extended Cabrera-Mott growth model. In this time, microwave losses scale linearly with the Nb2O5 thickness, with an extracted loss tangent tanδNb2O5 = 9.9×10 -3 . Our findings are of particular interest for devices spanning from superconducting qubits, quantum-limited amplifiers, microwave kinetic inductance detectors to single photon detectors.

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We report on a flexible 300 mm process that optimally combines optical and electron beam lithography to fabricate silicon spin qubits. It enables on-the-fly layout design modifications while allowing devices with either n-or p-type ohmic implants, a pitch smaller than 100 nm, and uniform critical dimensions down to 30 nm with a standard deviation ~ 1.6 nm.Various n-and p-type qubits are characterized in a dilution refrigerator at temperatures ~ 10 mK. Electrical measurements demonstrate well-defined quantum dots, tunable tunnel couplings, and coherent spin control, which are essential requirements for the implementation of a large-scale quantum processor.

The use of InGaAs as a high carrier mobility CMOS-channel material requires a proper electrical passivation of its interface with the gate dielectric. We investigate InGaAs passivation by Atomic Layer Deposition (ALD) of Al2O3, Gd2O3, and Sc2O3 using tri-methylaluminum (TMA), (iPrCp)3Gd, (MeCp)3Sc, and H2O as precursors. We discuss the impact of the starting precursor and TMA exposure during the initial cycles of Al2O3 on the interface trap density (Dit), frequency dispersion, leakage current, and breakdown field. Increasing the TMA pulse time to five seconds during the first five cycles reduce the Dit to 1.8 × 1012 eV−1 cm−2, while frequency dispersion, leakage current and breakdown field generally improve. Gd2O3 and Sc2O3 interfacial layers between InGaAs and Al2O3 are examined. The initial growth study of Gd2O3 ALD on InGaAs indicates growth inhibition as compared to the hydrophilic SiO2/Si substrate. Gd2O3 and Sc2O3 improve the interface in terms of Dit and border traps. The improvement depends on the initial precursor pulse lengths, and on the Gd- or Sc-content. The lowest Dit values, 2.5 × 1012 eV−1 cm−2 and 1.8 × 1012 eV−1 cm−2, are obtained for four cycles of Sc2O3 and Gd2O3, respectively. Interfacial self-cleaning by TMA, (iPrCp)3Gd, and (MeCp)3Sc is demonstrated by X-ray Photo-electron Spectroscopy and Time-of-flight secondary ion mass Spectroscopy.