Superconducting qubit based on superconducting circuits consists of a superconducting capacitor and a Josephson junction and with the transmon geometry is extensively used in advanced quantum processors, pursuing scalable quantum computing. The tuning of the qubit frequency of the transmon relies on magnetic flux dependent interference between the supercurrents of two superconductor-insulator-superconductor (S-I-S) Josephson junctions in a superconducting loop. Josephson junction based on superconductor-semiconductor-superconductor (S-Sm-S) materials opens up a possibility to the gate-tunable transmon, referred to as the "gatemon", in which the qubit frequency can be tuned by electrostatic mean. Recent realizations of gatemons on III-V material platforms show impressive development on the alternative to the transmon, yet still leave a big question on the scalability. The silicon-germanium (SiGe) heterostructure is one of the potential platforms to host hybrid devices due to its high hole mobility and the low Schottky barrier at the Ge-metal interface. Additionally, the compatibility with the silicon-based semiconductor industry is a capable advantage for the scaling-up qubit platform. In this thesis, I developed gatemons based on the Al-Ge-Al Josephson junction in a SiGe heterostructure. Firstly, the robust fabrication recipe, found on a top down approach, for Josephson Field Effect Transistors (JoFETs) is established. I performed measurements to study and characterize their properties as a function of the gate voltage, temperature, and magnetic field. Second, I developed the fabrication process to integrate Al-Ge-Al junctions shunted with capacitors and coupled to superconducting resonators. I demonstrated the first anticrossing features in one of the fabricated Ge gatemons. The resonant frequency of the gatemon is mapped using the two-tone spectroscopy technique and is found to be gate-tunable. The qubit has large spectral linewidth, implying a low coherence time. ​​​​​

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Contact : François Lefloch​
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