Periodic Reporting for period 3 - LONGSPIN (Long-range coupling of hole spins on a silicon chip) Reporting period: 2021-03-01 to 2022-08-31 Summary of the context and overall objectives of the project With the miniaturization of electronic devices, the semiconductor industry has to deal with complex technical barriers and is forced to introduce novel and innovative concepts. LONGSPIN is exactly in line with this new paradigm as it proposes to divert CMOS technology to explore a new path for quantum spintronics. Concretely the project aims at developping ultra-fast and ultra-coherent spin-orbit quantum bits (qubits).While spins are excellent quantum bits, their long-range coupling remains a challenge to tackle towards complex quantum computing architectures. LONGSPIN plans to take up this challenge using a microwave photon as a quantum mediator between spin-orbit qubits. The LONGSPIN project presents a unique approach by leveraging a standard silicon-on-insulator CMOS process for the implementation of the qubits co-integrated with superconducting microwave resonators.This research project will provide a CMOS quantum toolkit with optimized designs and materials for fast and coherent qubits with a profound understanding of the physical limitations to spin-orbit coherence and qubit gate fidelity in silicon. Eventually a microwave photon used as a quantum bus will allow the transfer of quantum information between distant spin-orbit qubits. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far The LONGSPIN team has equipped a dilution refrigerator to perform both state-of-the art spin qubits measurement as well as microwave resonator measurement in the single photon regime under static magnetic field.Measurements on hole spin-orbit qubit in silicon have allowed LONGPSIN to explore the physical mechanism behind the electrically driven spin resonance (Crippa et al. PRL 2018). With the understanding of this driving mechanism it should be possible to engineer devices to get faster and more coherent spin-orbit qubits.LONGSPIN also managed to readout a silicon hole spin-orbit qubit by low frequency dispersive gate reflectometry (Crippa et al. Nature Communications 2019). This readout proof-of-concept realized on an isolated double quantum dot should pave the way towards qubit readout in dense array of quantum dots.LONGSPIN has also started to co-integrate high impedance superconducting microwave resonator and CMOS silicon qubit devices. The resonators are made from Nobium Nitride thin films patterned as coplanar microwave cavities. Impedance as high as 4.5kOhms with internal quality factor above 20.000 under a static magnetic field of 1T has been demonstrated. These microwave cavity characteristics should allow the strong coupling of microwave photons and spin-orbit qubits towards long distance qubit interaction. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) The co-integration of CMOS spin-orbit qubit and microwave cavities goes beyond state of the art and should allow LONGSPIN to first perform fast single shot spin qubit dispersive readout and second to run circuit quantum electrodynamics experiments with spin-oribt qubits Artistic view of two CMOS spin-orbit qubit coupled via a microwave quantum bus
