We obtained remarkable results and achievements in all work packages. In the high-quality wires grown at our TUE partner we demonstrated strong spin-orbit coupling and hole-hole interactions and we observed superconducting proximity effects. TUE in collaboration with nanoPHAB explored the growth of Ge/Si core/shell channels in Si(111) and has revealed the optimum parameters allowing the start of the electronic properties tests. Superconductors have been grown on the Ge/Si core/shell nanowires. The measurements on these nanowires performed at UT, UBAS and IST have shown high-quality transport. The UBAS partner developed a radio-frequency (RF) charge sensing technique with exploitation potential: a voltage-tunable capacitor (varactor) suitable for single-shot charge and spin readout of quantum dots. In a joint effort involving the UT, UBAS and IST partners, we have made significant progress in understanding and maximizing the magnetic field resilience of the induced superconductivity and we demonstrated gate tuneable transmon devices in both platforms studied in TOPSQUAD: Ge-Si core-shell nanowires and the Ge quantum wells. The very large tunability of the qubit frequency, strong coupling with high-quality superconducting resonators and relaxation and coherence times that are on par with state-of-the-art type III-V gatemon devices constitute major achievements.
The consolidation of results, novel findings and productive interactions between all the partners led to 16 articles published in high impact journals like Nature Nanotechnology, Nano Letters, Nature Review Materials and Physical Review Letters. Recently, another 2 manuscripts have been submitted and 7 are in preparation.
The potential of the two young high-tech SMEs, Basel Precision Instruments (BASPI) and nanoPHAB, the main suppliers of the TOPSQUAD technologies, has been boosted thanks to the exploitation activities that took place within the project. BASPI focusses on high-sensitivity experiments and nanoPHAB provides unprecedented nanophotonic technologies. At the final stage of the project, multiple categories of exploitation are foreseen: (1) nanofabrication services for quantum physics applications (lead nanoPHAB), (2) nanopatterning of silicon on germanium devices (lead nanoPHAB) (3) high precision instruments for quantum transport experiments - Gate Leakage Current Measurement Box and Low-Noise High-Stability Voltage Preamplifier (lead BASPI), and at longer term (4) proof of concept of topological qubits for quantum computing applications.
