The coming revolution in quantum computing technologies creates some exciting challenges for engineers and equally exciting business opportunities for existing companies and new start-ups. One of these challenges is that existing superconducting quantum computers are already overcrowded with dense wiring and bulky microwave components, there is simply limited physical space in the dilution refrigerators. Moving to the 100-1000-qubit level and beyond requires new solutions for scalable and cost-effective microwave control and measurement circuity. Simply put, the microwave control systems need to be of much lighter weight and smaller physical size than at present with a high level of integration while being cost-effective and energy efficient. Some of the critically required cryogenic microwave control components are dense wiring, attenuators, and circulators, which are used to bring control signals from the electronics into the cryostat, to allow the transmission of desired frequency bands while rejecting unwanted bands and to protect quantum processors against reflected signals and decoherence. Typically, dense wiring connections, filters and circulators occupy quite a large size in the cryostat and the number of them needed is growing rapidly as we scale up the number of qubits. For example, in order to scale to 1-million-qubit-computer, the control system would also need 1-10 million filters, circulators, and coaxial cables, occupying more than three football fields of floor space and consume roughly 40 MW of dc power (assuming no power loss associated with signal distribution). It is vital to develop miniature, low-cost, reliable, insertion loss and highly integrated microwave technologies for superconducting quantum computing for the UK to be successful in this rapidly growing sector, with a projected global market of £4B by 2024. In order to move to the 100s-qubit level and beyond, where quantum computing becomes truly useful, innovation for scalable microwave control systems is needed. A short time-window is available for the UK to invest in real-world demonstration of superconducting quantum computing. Without this, the potential for a UK researcher to lead the world in this emerging area and build strong academic and industrially facing leadership will be lost. My fellowship aims to bring modern microwave approaches to supercondcting quantum computing and demonstrate improved quantum pefromance with reduced hardware overheads and thermal loaads, paving the way to move towards 100s-qubit level, where quantum computing becomes truly useful

In the last decade, proof of concepts has been given and small-scale demonstrators have been built to show that the quantum devices allow obtaining unprecedented performances in practical applications. For example, dramatic enhancements can be obtained in the speed and computational power of next-generation computers (Quantum computing) using superconducting qubits. Also, disruptive performance improvements can be achieved in advanced imaging, remote sensing, long distance/secure communication (quantum cryptography) or diagnostic techniques using superconducting nanowire single-photon detectors - SNSPDs. The transition from demonstrators to practical scaled-up devices with a large number of elements is still at an early stage and a significant technological leap is required for a real breakthrough in those fields. The identified challenge in scaling-up the number of elements in quantum circuits, that is virtually identical for superconducting qubits and SNSPDs operating in Radio Frequency regime - RF-SNSPDs -, is represented by efficient multiplexing of these elements since they typically operate at cryogenic temperatures and need multiple connections for control and read-out at microwave frequencies. This makes the electronics complex, costly and difficult to scale beyond 10 to 100 of elements in the commercially available cryostats hampering their use in real-world applications. Single Flux Quantum (SFQ) electronics can operate at cryogenic temperature with unrivalled high frequency and ultra-low power consumption relying on the peculiar current to voltage relation of their basic element: the Josephson Junctions (JJ). Under proper condition, JJs generates ~2 ps width voltage pulses at repetition frequency above 500 GHz, with unprecedented time accuracy, stability and low power consumption. SFQ electronics is intrinsically scalable and we propose to use generated SFQ pulses as a source for precise and low noise frequency signals for multiplexed control and read-out of on-chip integrated qubits and RF-SNSPDs arrays. This transformative approach will allow to finally fill the gap in the existing quantum technology for a step-change at the same time in quantum science and advanced sensing applications. At this aim, we will bring together top UK expertise in nanofabrication and superconducting quantum technology, backed by a strong commitment from the UK world-leading company in SFQ electronics and quantum technologies SeeQC UK. We build on previous work carried out through Innovate UK, Marie Curie, Royal Society and European Research Council funding and make complimentary use of expertise and nanofabrication facilities to significant progress in the development of quantum technology in a 3-years targeted programme. Thanks to the strategic collaboration with National UK Quantum Technology Hubs, we will carry out joint experiments in quantum computing/simulation (Hub in Quantum computing and simulation - HQCS) and in advanced imaging (QuantIC) applications to show the game-changing nature of developed technology. Also, we will leverage support to engage closely with end-users and stakeholder maximizing the impact of the research project. Potential markets for developed technology will be exploited through the collaboration with QT hubs industry partners' network and with the strategic Industrial partners of this proposal like Kelvin Nanotechnology (KNT), Oxford Quantum Circuits (OQC) and SeeQC UK. This project is designed to generate high-quality research outputs and to deploy advanced technology in the field of quantum science. The work strongly resonates with the central themes of Horizon 2020 programmes and with the UK strategic research priorities set by Research Councils. The long-term goal is to establish a world-class experimental research programme which will have a powerful cross-disciplinary impact strengthening the UK's leading position in new science and technology to generate societal and economic benefits.

The EPSRC Quantum Computing and Simulation Hub will enable the UK to be internationally leading in Quantum Computing and Simulation. It will drive progress toward practical quantum computers and usher in the era where they will have revolutionary impact on real-world challenges in a range of multidisciplinary themes including discovery of novel drugs and new materials, through to quantum-enhanced machine learning, information security and even carbon reduction through optimised resource usage. The Hub will bring together leading quantum research teams across 17 universities, into a collaboration with more than 25 national and international commercial, governmental and academic entities. It will address critical research challenges, and work with partners to accelerate the development of quantum computing in the UK. It will foster a generation of UK-based scientists and engineers equipped with the new skill sets needed to make the UK into a global centre for innovation as the quantum sector emerges. The Hub will engage with government and citizens so that there is a wide appreciation of the potential of this transformative technology, and a broad understanding of the issues in its adoption. Hub research will focus on the hardware and software that will be needed for future quantum computers and simulators. In hardware we will advance a range of different platforms, encompassing simulation, near term quantum computers, and longer term fully scalable machines. In software the Hub will develop fundamental techniques, algorithms, new applications and means to verify the correct operation of any future machine. Hardware and software research will be closely integrated in order to provide a full-stack capability for future machines, enabled by the broad expertise of our partners. We will also study the architecture of these machines, and develop emulation techniques to accelerate their development. Success will require close engagement with a wide range of commercial and government organisations. Our initial partners include finance (OSI), suppliers (Gooch & Housego, Oxford Instruments, E6), integrators and developers (OQC, QM, CQC, QxBranch, D-Wave), users from industry (Rolls-Royce, Johnson Matthey, GSK, BT, BP, TrakM8, Airbus, QinetiQ) and government (DSTL, NCSC), and other research institutions (NPL, ATI, Heilbronn, Fraunhofer). We will build on this strong network using Industry Days, Hackathons and targeted workshops, authoritative reports, and collaborative projects funded through the Hub and partners. Communications and engagement with the community through a range of outreach events across the partnership will inform wider society of the potential for quantum computing, and we will interact with policy makers within government to ensure that the potential benefits to the UK can be realised. The Hub will train researchers and PhD students in a wide range of skills, including entrepreneurship, intellectual property and commercialisation. This will help deliver the skilled workforce that will be required for the emerging quantum economy. We will work with our partners to deliver specific training for industry, targeting technical, commercial and executive audiences, to ensure the results of the Hub and their commercial and scientific opportunities are understood. The Hub will deliver demonstrations, new algorithms and techniques, spinout technologies, and contribute to a skilled workforce. It will also engage with potential users, the forthcoming National Centre for Quantum Computing, the global QC community, policy makers and the wider public to ensure the UK is a leader in this transformative new capability.