Following the consolidation of a trans-institutional research team of around 50 people (staff engineers, researchers, technicians, PhD students and post-docs), research efforts have focused on developing the building blocks of a scalable quantum processor based on semiconductor spin qubits. In work-package (WP) 1, devoted to device fabrication and basic characterization, priority was given to the development of a new gate stack consisting of two overlapping gate layers, with the goal to increase the electrical tunability of our MOS quantum dots. In WP 2, we worked on the study and improvement of qubit basic functionalities (initialisation, control, readout) and performance (coherence, control speed, etc.). Using rf reflectometry techniques we achieved high-fidelity spin readout on microsecond time scale. In the case of hole spin qubits, the improved device quality enabled us to access the few-hole regime with unprecedented agreement between measured and simulated spin properties. We revealed the existence of operational sweet spots with hole-spin coherence times as high as 88 microseconds, i.e. well beyond the state-of-the-art. We also showed that the sweet-spot condition can be established while simultaneously maximising the qubit control efficiency resulting in an optimal operation regime yielding high qubit fidelity. In WP3, we explored the possibility of coupling hole spin qubits to microwave photons in superconducting resonators. We observed a very strong spin-photon coupling exceeding 300 MHz, which opens great prospects for using microwave resonators to perform non-demolition spin readout or to couple hole spin qubits far away from each other. As an alternative approach to long-range coupling, we also investigated the use of electron shuttling using GaAs multi-dot devices as a test bench. Finally, we worked on the development of cryogenic electronics to be integrated with quantum processors through specially designed interposers embedding superconducting interconnections.
