The internet data rate of Mb/s is currently available to UK homes thanks to installation of fibre network. Recently Fujitsu, a major telecom company, outlined their plan to lay Gb/s fibre network in UK, which can increase the data rate to 10 Gb/s and beyond. Therefore optical fibre will play an ever increasing importance in our life and hence there is a clear need to carry out research in ultrafast optical components such as photodiodes, used to convert optical signal to electrical signal. In photodiodes the energy from light is used to release an electron from an atom and a detectable current is generated when the electron is swept by an electric field. In a specially designed avalanche photodiode (APD) the electric field is increased such that a single electron generated by the photoelectric effect can produce an avalanche of electrons and holes. Consequently a much larger signal is produced, leading to a better signal to noise ratio. Unfortunately current commercial APD can only work up to 10 Gb/s and is therefore not future proof. In this proposal, we will develop extremely thin 10-50 nm semiconductor layer to achieve the avalanche effect at ps time scale such that our APDs can operate at bit rates of Tb/s. The new semiconductor materials that will be developed in this project are AlAsSb and AlGaPSb since they have great potential to withstand extremely high electric field while maintaining low dark current (essential to minimise errors in digital signal). Crucially since our materials are only nm thick, we can engineer the electric field in APD to impose some degree of coherence in the electron and hole behaviours so that the avalanche effect occurs with minimal noise. We believe our APDs can be designed to approach the performance of an ideal noiseless APD with high bandwidth for optical communications. We recently demonstrated that the avalanche effect in thin AlAsSb is relatively immune to temperature change. Therefore in addition to ultra high speed optical communication, our proposed nm scaled AlAsSb and AlGaPSb avalanche layers are envisaged to work as an ultra fast photon counter with high immunity to ambient temperature fluctuation. Since a photon is the basic unit of light, the "ultimate" light sensor is achieved by increasing the avalanche gain to approximately a million so that the APD works as a photon counter. Our thin avalanche layer has the potential to register a photon count in a few ps, which is at least an order of magnitude faster than current APD photon counters. If successful one of the major impacts of our photon counter will be to improve the data encryption technique called quantum key distribution in which the data is encrypted using a single photon. This is believed to be the most secure encryption technology. Any unauthorised detection of the photon will cause a significant error rate, and hence alerting the sender of the attempted hacking. Therefore the high thermal stability and fast response time of our APDs will enhance the robustness of future quantum cryptography systems. We also believe our new technology will bring significant improvement to medical X-ray imaging as the APD can improve the signal to noise ratio of X-ray detection system. Typically the avalanche effect increases the electrical signal, induced by the X-ray absorption, to above the electronic circuit noise and hence enhancing the image quality. Our recent work showed that having a thin avalanche layer is essential for high performance X-ray APD. Hence our work will enable a new generation of X-ray APDs for imaging applications. To achieve the goals discussed above we will carry out very systematic development of AlAsSb and AlGaPSb APDs via advanced growth of the semiconductor crystals and optimised chemical etching process as well as meticulous measurements to extract key material properties for design of high performance APDs utilising nm avalanche regions.

Quantum technologies (QT) are new, disruptive information technologies that can outperform their conventional counterparts, in communications, sensing, imaging and computing. The UK has already invested significantly in a national programme for QT, to develop and exploit these technologies, and is now investing further to stimulate new UK industry and generate a supply of appropriately skilled technologists across the range of QT sectors. All QT exploit the various quantum properties of light or matter in some way. Our work is in the communications sector, and is based on the fundamental effect that measuring or detecting quantum light signals irreversibly disturbs them. This effect is built into Nature, and will not go away even when technologies (quantum or conventional) are improved in the future. The fundamental disturbance of transmitted quantum light signals enables secure communications, as folk intercepting signals when they are not supposed to (so-called eavesdroppers) will always get caught. This means Alice and Bob can use quantum light signals to set up secure shared data, or keys, which they can then use for a range of secure communications and transactions - this is quantum key distribution (QKD). The irreversible disturbance of light can also be used to generate random numbers - another very important ingredient for secure communications, cryptology, simulation and modelling. In the modern world where communications are so ubiquitous and important, there is increasing demand for new secure methods. Technologies and methods widely used today will be vulnerable to emergent quantum computing technologies, so encrypted information being sent around today which has a long security shelf-life will be at risk in the future. New "quantum safe" methods that are not vulnerable to any future QT have to be developed. So QKD and new mathematical encryption must be made practical and cost effective, and soon. The grand vision of the Quantum Communications Hub is therefore to pursue quantum communications at all distance scales, to offer a range of applications and services and the potential for integration with existing infrastructure. Very short distance communications require free space connections for flexibility. Examples include between a phone or other handheld device and a terminal, or between numerous devices and a fixed receiver in a room. The Hub will be engineering these "many-to-one" technologies to enhance practicality and real-world operation. Longer distance conventional communications - at city, metropolitan and inter-city scales - already use optical fibres, and quantum communications have to leverage and complement this. The Hub has already established the UK's first quantum network, the UKQN. We will be extending and enhancing the UKQN, adding function and capability, and introducing new QKD technologies - using quantum light analogous to that used in conventional communications, or using entanglement working towards even longer distance fibre communications. The very longest distance communications - intercontinental and across oceans - require satellites. The Hub will therefore work on a new programme developing ground to satellite QKD links. Commercial QKD technologies for all distance scales will require miniaturisation, for size, weight and power savings, and to enable mass manufacture. The Hub will therefore address key engineering for on-chip operation and integration. Although widely applicable, key-sharing does not provide a solution for all secure communication scenarios. The Hub will therefore research other new quantum protocols, and the incorporation of QKD into wider security solutions. Given the changing landscape worldwide, it is becoming increasingly important for the UK to establish national capability, both in quantum communication technologies and their key components such as light sources and detectors. The Hub has assembled an excellent team to deliver this capability.

Single-photon counting - the ability to faithfully capture the single quantum of light - is a critical capability for a wide range of new low-light sensing applications and a host of emerging photonic quantum technologies. This proposed Programme Grant aims to significantly expand the operational region of single-photon detectors well beyond silicon's 1000nm wavelength limit into the short-wave infrared (SWIR) region of wavelengths between 1400nm to 3000nm, and part of the mid-wave infrared (MWIR) region between 3000nm and 5000nm. By scaling up SWIR and MWIR semiconductor and superconductor single-photon detectors to large area focal plane arrays, we will produce revolutionary new cameras with picosecond timing resolution which can be used, for example, to see though fog in automotive lidar scenarios, as well as allowing imaging and sensing in new applications in environmental monitoring, healthcare, and security and defence. The project will involve the design and fabrication of innovative new detector platforms of Ge-on-Si and III-V semiconductor detectors. The detectors are capable of single-photon sensitivity in the SWIR and MWIR regions, and will be fabricated in detector array format. We will also examine superconducting nanowires to expand their operation into the MWIR regions and fabricate arrayed detector configurations. A key part of the project is to integrate these arrayed detector technologies with read-out circuitry capable of rapid, low latency delivery of single-photon data. In addition, we will utilise micro-optic technology to optimise detection efficiency and demonstrate multiple wavelength filtering. The cameras will be designed for use in a range of applications areas, including lidar, where the time-of-flight of the return photons can be used for the measurement of distance. In arrayed detector format, we will make cameras from which we will demonstrate three-dimensional imaging at long distance, where the sensitivity and time-resolution will enhance imaging through dense fog and other obscurants. We will demonstrate our detector technologies in quantum cryptography applications, where encryption keys can be shared between two users. By sending data encoded in single-photons it is possible for the sender and receiver to share a secure, random key known only to them. The most critical component in this form of quantum communication is the single-photon detector - we will demonstrate the use of our detectors both in optical fibre and free-space quantum key distribution scenarios. Other emerging applications in spectroscopy and biophotonics will be demonstrated.

We aim to grow the world's leading centre for training in quantum engineering for the emerging quantum technology (QT) industry. We have designed this CDT in collaboration with a large number of academic and industry experts, and included as partners those who will add substantially to the training and cohort experience. Through this process a consistent picture of what industry wants in future quantum engineers emerged: people who can tackle the hardest intellectual challenges, recognising the end goal of their research, with an ability to move from fundamental physics towards the challenges of engineering and miniaturising practical systems, who understands the capabilities of other people (and why they are useful). Industry wants people with good decision-making, communication and management skills, with the ability to work across discipline boundaries (to a deadline and a budget!) and build interdisciplinary teams, with the ability to translate a problem from one domain to another. Relevant work experience, knowledge of entrepreneurship, industrial R&D operations and business practices are essential. By forming a hub of unrivalled international excellence in quantum information and photonics, surrounded by world-class expertise in all areas of underpinning science and technology and the scientific and technological application areas of QT, and a breadth of academic and industry partners, we will deliver a new type of training: quantum engineering. Bristol has exceptional international activity in the areas that surround the hub: from microelectronics and high performance computing to system engineering and quantum chemistry. The programme will be delivered in an innovative way-focussing particularly on cohort learning-and assessed by a variety of different means, some already in existence in Bristol. We believe that we are attempting something new and exciting that has the potential to attract and train the best students to ensure that the resulting capacity is world-class, thus providing real benefits to the UK economy.

The 2015 UK National Security Strategy identifies cyber security as one of the top four UK national security priorities. The UK National Cyber Security Strategy 2016-2021 (NCSS) has an underlying vision to make the UK secure and resilient to cyber threats, prosperous and confident in the digital world. It is widely recognised that the UK, indeed the world, is short of cyber security specialists. Cyber security is genuinely cross-disciplinary. It's about technology, and the networks and systems within which technology is deployed. But it's also about society and how it engages with technology. Researching the right questions requires researchers to fully understand the integrated nature of the cyber security landscape. A CDT provides the perfect vehicle within which suitably broad training can be provided. The establishment of a cohort of researchers with different backgrounds and experience allows this knowledge to be cultivated within a rich environment, where the facts of hard science can be blended with the perspectives and nuances of more social dimensions. While society has made progress in developing the technology that underpins security, privacy and trust in cyberspace, we lag behind in our understanding of how society engages with this technology. Much more fundamentally, we don't even really understand how society engages with the concepts of security, privacy and trust in the first place. We will host a CDT in Cyber Security for the Everyday, which signals that research in our CDT will focus on the technologies deployed in everyday digital systems, as well as the everyday societal experience of security. Research in our CDT will investigate the security of emerging technologies. As cyberspace continues to evolve, so, too, do the technologies required to secure its future. Research topics include the cryptographic tools that underpin all security technologies, the security of the systems within which these tools are deployed, the use of artificial intelligence to aid discovery of system vulnerabilities, and security and privacy of everyday objects which are becoming embedded in cyberspace. Our CDT will also research how to secure cyber societies. Securing increasingly networked, automated, and autonomous societies requires an integrated research approach which engages the social, technological, cultural, legal, social-psychological and political on equal terms. Research topics include exploring state, institutional and corporate responsibility over how information is gathered and used, investigating how cyber security is perceived, understood and practiced by different communities, and researching how social differences and societal inequalities affect notions of, and issues relating to, cyber security. Our training programme will be based around a suite of relevant masters programmes at Royal Holloway, including in Information Security, Geopolitics and Security, and Data Science. This will be supplemented by workshops, practice labs, and a comprehensive generic skills programme. Students will work closely with the wider cyber security community through a series of industry engagement sessions and visits, summer projects, and three-month internships. Peer-to-peer learning will be fostered through group challenges, workshop design and delivery, reading groups and a social programme.