thesis published Oliver Sagi author 71616374-A8E9-11E9-A7CA-09ECE5697425 Georgios Katsaros supervisor GradSch department GeKa department Merging spin and superconducting qubits in planar Ge project High impedance circuit quantum electrodynamics with hole spins project Hybrid Semiconductor - Superconductor Quantum Devices project TOPOLOGICALLY PROTECTED AND SCALABLE QUANTUM BITS project The new era of Ge has opened up new possibilities in quantum computing. The maturity of Ge spin qubits is unquestioned, while hybrid semiconductor-superconductor Ge circuits are on track to enter the game. Gate-tunable transmons (gatemons) employing semiconductor Josephson junctions have recently emerged as building blocks for such hybrid quantum circuits. In this thesis, we present a gatemon fabricated in planar Germanium. We induce superconductivity in a two-dimensional hole gas by evaporating aluminum atop a thin spacer, which separates the superconductor from the Ge quantum well. The Josephson junction is then integrated into an Xmon circuit and capacitively coupled to a transmission line resonator. We showcase the qubit tunability in a broad frequency range with resonator and two-tone spectroscopy. Time-domain characterizations reveal energy relaxation and coherence times up to 75 ns. Our results, combined with the recent advances in the spin qubit field, pave the way towards novel hybrid and protected qubits in a group IV, CMOS-compatible material. https://research-explorer.ista.ac.at/download/18076/18093/OliverSagi_Thesis_pdfa.pdf application/pdfno https://research-explorer.ista.ac.at/download/18076/18094/Thesis_OliverSagi.zip application/x-zip-compressed Institute of Science and Technology Austria2024 eng 2663-337X10.15479/at:ista:18076 111 https://research-explorer.ista.ac.at/record/17202 Sagi, O. (2024). <i>Hybrid circuits on planar Germanium</i>. Institute of Science and Technology Austria. <a href="https://doi.org/10.15479/at:ista:18076">https://doi.org/10.15479/at:ista:18076</a> Sagi, Oliver. <i>Hybrid Circuits on Planar Germanium</i>. Institute of Science and Technology Austria, 2024, doi:<a href="https://doi.org/10.15479/at:ista:18076">10.15479/at:ista:18076</a>. O. Sagi, “Hybrid circuits on planar Germanium,” Institute of Science and Technology Austria, 2024. Sagi O. 2024. Hybrid circuits on planar Germanium. Institute of Science and Technology Austria. Sagi O. Hybrid circuits on planar Germanium. 2024. doi:<a href="https://doi.org/10.15479/at:ista:18076">10.15479/at:ista:18076</a> O. Sagi, Hybrid Circuits on Planar Germanium, Institute of Science and Technology Austria, 2024. Sagi, Oliver. “Hybrid Circuits on Planar Germanium.” Institute of Science and Technology Austria, 2024. <a href="https://doi.org/10.15479/at:ista:18076">https://doi.org/10.15479/at:ista:18076</a>. 180762024-09-16T12:58:36Z2025-10-15T06:31:48Z