The elementary unit of quantum information is the quantum bit or qubit. Like the classical bit, the qubit is a two-level system but with the intriguing ability to exist in a superposition of states. This means it can be in the on and off state at the same time which has profound implications if we consider quantum systems of more than one qubit. Instead of each qubit carrying any well-defined information of its own, the information is encoded in their joint properties. In quantum mechanics, the qubits are described as being entangled. The challenge is to find ways to harness quantum phenomena such as superposition and entanglement to construct a quantum computer that is able to perform computational tasks that are unattainable in a classical context. A very natural qubit is the electron spin. The energy difference between spin states of an electron can be precisely controlled by magnetic fields and, using the electron's charge, it is also possible to isolate and manipulate individual spins electrically. One route to achieve entanglement between spin qubits is to use the interaction of their electron wavefunction overlap by placing them in close proximity. While such an approach is feasible for a small number of qubits, a large-scale quantum processor which relies on direct nearest neighbour coupling becomes rapidly impractical. Here we therefore propose an alternative strategy which makes use of an intriguing quantum mechanical effect by which two spatially separated quantum bits become entangled if a measurement cannot tell them apart. As has been shown theoretically, measurement-based entanglement can be used to couple large numbers of physically separated qubits, building up so-called graph states. Computation is then achieved by a sequence of measurements on individual qubits that consumes the entanglement - known as one-way quantum computation - which is entirely different from the standard circuit-based approach. In practise this also requires the presence of a quantum memory where quantum information is stored to allow graph-state growth without the risk of losing existing entanglement. Here we propose to use a solid-state implementation which is ideally suited to this task: single As-dopants in isotopically pure Si-28. To fabricate the devices, we will use the most precise silicon dopant incorporation technique available: scanning tunnelling microscopy (STM) hydrogen resist lithography. The atomically precise incorporation of individual As-dopants is essential in satisfying a key requirement of the measurement-based entanglement protocol: qubit indistinguishability. Having fabricated the devices, we will be able to manipulate the electron spins of the As-dopants and create entanglement between remote qubits using projective measurements. For this we will be using radio-frequency reflectometry techniques which allows us to perform these tasks on a timescale significantly faster than electron spin lifetimes. Once entanglement generation has been achieved, hyperfine coupling will be used to transfer the quantum information from the electron to the As nuclear spin states. This approach takes advantage of record nuclear spin coherence, in the 10-100 second range, of dopants in Si and allows us to grow the entangled graph state. Moreover, since the As nucleus has a non-zero electric quadrupole moment and a four dimensional Hilbert space we will be able to control the nuclear spins electrically and store and control the equivalent of two qubits in each dopant. For a proof-of-principle demonstrator we will entangle four spatially separated devices, each consisting of two As-dopant atom qubits with all-to-all qubit connectivity, equivalent to a 16-qubit processor. The experimental efforts will be supported by theoretical studies to further develop the most efficient strategies for growing a resilient remote network taking into account realistic experimental parameters such as spin dephasing and signal loss.

The primary objective of the QC2 CDT is to train the upcoming generation of pioneering researchers, entrepreneurs, and business leaders who will contribute to positioning the UK as a global leader in the quantum-enabled economy by 2033. The UK government and industry have demonstrated their commitment by investing £1 billion in the National Quantum Technologies Programme (NQTP) since 2014. In its March 2023 National Quantum Strategy document, the UK government reaffirmed its dedication to quantum technologies, pledging £2.5 billion in funding over the next decade. This commitment includes the establishment of the UKRI National Quantum Computing Centre (NQCC). The fields of quantum computation and quantum communications are at a pivotal juncture, as the next decade will determine whether the long-anticipated technological advancements can be realized in practical, commercially-viable applications. With a wide-ranging spectrum of research group activities at UCL, the QC2 CDT is uniquely situated to offer comprehensive training across all levels of the quantum computation and quantum communications system stacks. This encompasses advanced algorithms and quantum error-correcting codes, the full range of qubit hardware platforms, quantum communications, quantum network architectures, and quantum simulation. The QC2 CDT has been co-developed through a partnership between UCL and a network of UK and international partners. This network encompasses major global technology giants such as IBM, Amazon Web Services and Toshiba, as well as leading suppliers of quantum engineering systems like Keysight, Bluefors, Oxford Instruments and Zurich Instruments. We also have end-users of quantum technologies, including BT, Thales, NPL, and NQCC, in addition to a diverse group of UK and international SMEs operating in both quantum hardware (IQM, NuQuantum, Quantum Motion, SeeQC, Pasqal, Oxford Ionics, Universal Quantum, Oxford Quantum Circuits and Quandela) and quantum software (Quantinuum, Phase Craft and River Lane). Our partners will deliver key components of the training programme. Notably, BT will deliver training in quantum comms theory and experiments, IBM will teach quantum programming, and Quantum Motion will lead a training experiment on semiconductor qubits. Furthermore, 17 of our partners will co-sponsor and co-supervise PhD projects in collaboration with UCL academics, ensuring a strong alignment between the research outcomes of the CDT and the critical research objectives of the UK quantum economy. In total the cash and in-kind contributions from our partners exceed £9.1 million, including £2.944 million cash contribution to support 46 co-sponsored PhD studentships. QC2 will provide an extensive cohort-based training programme. Our students will specialize in advanced research topics while maintaining awareness of the overarching system requirements for these technologies. Central to this programme is its commitment to interdisciplinary collaboration, which is evident in the composition of the leadership and supervisory team. This team draws expertise from various UCL departments, including Chemistry, Electronics and Electrical Engineering, Computer Science, and Physics, as well as the London Centre for Nanotechnology (LCN). QC2 will deliver transferable skills training to its students, including written and oral presentation skills, fostering an entrepreneurial mindset, and imparting techniques to maximize the impact of research outcomes. Additionally, the programme is committed to taking into consideration the broader societal implications of the research. This is achieved by promoting best practices in responsible innovation, diversity and inclusion, and environmental impact.

Quantum Technology is based on quantum phenomena that govern physics on an atomic scale, enabling key breakthroughs that enhance the performance of classical devices and allow for entirely new applications in communications technology, imaging and sensing, and computation. Quantum networks will provide secure communication on a global scale, quantum sensors will revolutionise measurements in fields such as geology and biomedical imaging, and quantum computers will efficiently solve problems that are intractable even on the best future supercomputers. The economic and societal benefit will be decisive, impacting a wide range of industries and markets, including engineering, medicine, finance, defence, aerospace, energy and transport. Consequently, Quantum Technologies are being prioritised worldwide through large-scale national or trans-national initiatives, and a healthy national industrial Quantum Technology ecosystem has emerged including supply chain, business start-ups, and commercial end users. Our Centre for Doctoral Training in Applied Quantum Technologies (CDT-AQT) will address the national need to train cohorts of future quantum scientists and engineers for this emerging industry. The training program is a partnership between the Universities of Strathclyde, Glasgow and Heriot-Watt. In collaboration with more than 30 UK industry partners, CDT-AQT will offer advanced training in broad aspects of Quantum Technology, from technical underpinnings to applications in the three key areas of Quantum Measurement and Sensing, Quantum Computing and Simulation, and Quantum Communications. Our programme is designed to create a diverse community of responsible future leaders who will tackle scientific and engineering challenges in the emerging industrial landscape, bring innovative ideas to market, and work towards securing the UK's competitiveness in one of the most advanced and promising areas of the high-tech industry. The quality of our training provision is ensured by our supervisors' world-class research backgrounds, well-resourced research environments at the host institutions, and access to national strategic facilities. Industry engagement in co-creation and co-supervision is seen as crucial in equipping our students with the transferable skills needed to translate fundamental quantum physics into practical quantum technologies for research, industry, and society. To benefit the wider community immediately, we will make Quantum Technologies accessible to the general public through dedicated outreach activities, in which our students will showcase their research and exhibit at University Open Days, schools, science centres and science festivals.

The emergence and re-emergence of infectious diseases is one of the greatest threats to human health. By their very nature, outbreaks of infectious disease can spread rapidly, causing enormous losses to health and livelihood. For example, an estimated 35-million people are HIV-infected, antibiotic resistant pathogens such as MRSA are a major global public health problem and pandemic influenza is rated as the greatest national risk on the UK government risk register (Cabinet Office 'National Risk Register for Civil Emergencies 2012 Edition'). Early diagnosis plays a vital role in the treatment, care and prevention of infectious diseases. However worldwide, many infections remain undiagnosed and untreated or are diagnosed at the late stage due to poor diagnostic tools, resulting in on-going transmission of serious infections or delay in the identification of emerging threats, leading to major human and economic consequences for millions of people. Our vision is to establish an EPSRC Interdisciplinary Research Centre to create a new generation of early-warning sensing systems to diagnose, monitor & prevent the spread of infectious diseases. This large scale collaboration will bring together scientists, engineers and computer scientists from University College London, Imperial College, London School of Hygiene and Tropical Medicine and the University of Newcastle together with NHS stakeholders, the Health Protection Agency and industry partners. Working across and beyond traditional research boundaries, the IRC will pioneer innovative nano-enabled mobile diagnostic tests which can be used in GP surgeries, community settings and developing countries, linked to smart digital-surveillance systems which search for information on the web to detect early indicators of diseases. The tremendous expansion in mobile phone technology with an estimated 6 billion users worldwide, provides new opportunities for point-of-care diagnostics with inbuilt capacity to securely transmit results to public healthcare systems. The challenge is to create robust multimarker sensor platforms that can diagnose early infections with high sensitivity and specificity. Our strategy will seamlessly integrate the scientific excellence underpinning recent breakthroughs by our team in diverse areas of biomarker discovery, capture coatings, nanoparticles, nanopatterning, sensor systems, wireless connectivity, data mining and health economic analysis of diagnostics. Moreover we will explore innovative new strategies to search for early indicators of infection (herein we coin the phrase "e-markers") by searching through millions of web-accessible information sources including Google, Facebook and Twitter to identify outbreaks even from people who do not attend clinics or from geographical regions that are invisible to traditional public health efforts. By providing doctors, community workers and public health organisations with real-time, geographically-linked information about emerging infections which will be visualised on a "dashboard" display, we will support more rapid, stratified, integrated evidence-based interventions, benefitting individuals and populations. Our disruptive early warning sensing capabilities will bring major human and economic benefits to the NHS and global healthcare systems. The ultimate beneficiaries will be patients since early diagnosis will empower them to gain faster access to better treatments, helping to reduce suffering and risk of death. Society will benefit by preventing the onwards spread of infection by people who are unaware of their infection and preserve the effectiveness of precious antimicrobial medicines for future generations. The NHS and healthcare systems will benefit by simplifying patient pathways allowing tests and results to be given in a single visit and so provide a more cost-effective solution of community based care. Our technologies will also provide new commercial opportunities for British industry.