The description of the laws of quantum mechanics saw a transformation in society's understanding of the physical world-for the first time we understood the rules that govern the counterintuitive domain of the very small. Rather than being just passive observers now scientists are using these laws to their advantage and quantum phenomena are providing us with methods of improved measurement and communication; furthermore they promise a revolution in the way materials are simulated and computations are performed. Over the last decade significant progress has been made in the application of quantum phenomena to meeting these challenges. This "Engineering Photonic Quantum Technologies" Programme Grant goes significantly beyond previous achievements in the quantum technology field. Through a series of carefully orchestrated work packages that develop the underlying materials, systems engineering, and theory we will develop the knowledge and skills that enable us to create application demonstrators with significant academic and societal benefit. For the first time in quantum technologies we are combining materials and device development and experimental work with the important theoretical considerations of architectures and fault tolerant approaches. Our team of investigators and partners have the requisite expertise in materials, individual components, their integration, and the underpinning theory that dictates the optimal path to achieving the programme goals in the presence of real-world constraints. Through this programme we will adopt the materials systems most capable of providing application specific solutions in each of four technology demonstrations focused on quantum communications, quantum enhanced sensing, the construction of a multiplexed single-photon source and information processing systems that outperform modern classical analogues. To achieve this, our underlying technology packages will demonstrate very low optical-loss waveguides which will be used to create the necessary 'toolbox' of photonic components such as splitters, delays, filters and switches. We will integrate these devices with superconducting and semiconducting single-photon detector systems and heralded single-photon sources to create an integrated source+circuit+detector capability that becomes the basis for our technology demonstrations. We address the challenge of integrating these optical elements (in the necessary low-temperature environment) with the very low latency classical electronic control systems that are required of detection-and-feedforward schemes such as multiplexed photon-sources and cluster-state generation and computation. At all times a thorough analysis of the performance of all these elements informs our work on error modelling and fault tolerant designs; these then inform all aspects of the technology demonstrators from inception, through decisions on the optimal materials choices for a system, to the layout of a circuit on a wafer. With these capabilities we will usher in a disruptive transformation in ICT. We will demonstrate mutli-node quantum key distribution (QKD) networks, high-bit rate QKD systems with repeaters capable of spanning unlimited distances. Our quantum enhanced sensing will surpass the classical shot noise limit and see the demonstration of portable quantum-enhanced spectroscopy system. And our quantum information processors will operate with 10-qubits in a fault tolerant scheme which will provide the roadmap to 1,000 qubit cluster state computing architectures.

The project seeks to take the Athermal Laser research carried out at the University of Cambridge and develop further so that it is at a suitable point for commercial evaluation. The technical develop will involve optimized design, outsourced commercial device prototype fabrication and control hardware and software development. It is anticipated that commercial consultants will be employed to carry out market survey and targeted marketing activities in tandem with Cambridge Enterprise.

It is recognised that global communication systems are rapidly approaching the fundamental information capacity of current transmission technologies. Saturation of the capacity of the communication systems might have detrimental impact on the economy and social progress and public, business and government activities. The aim of the proposed research is to develop, through theory and experiment, disruptive approaches to unlocking the capacity of future information systems that go beyond the limits of current optical communications systems. The research will combine techniques from information theory, coding, study of advanced modulation formats, digital signal processing and advanced photonic concepts to make possible breakthrough developments to ensure a robust communications infrastructure beyond tomorrow. Increasing the total capacity of communication systems requires a multitude of coordinated efforts: new materials and device bases, new fibres, amplifiers and network paradigms, new ways to generate, transmit, detect and process optical signals and information itself - all must be addressed. In particular, the role of fibre communications, providing the capacity for a lion share of the total information traffic, is vital. One of the important directions to avoid the so-called "capacity crunch", the exhaust in fibre capacity - is to develop completely new transmission fibres and amplifiers. However, there is also a growing need for complimentary actions - innovative and radically novel approaches to coding, transmission and processing of information. Our vision is focused on the need to quantify the fundamental limits to the nonlinear channels carried over optical fibres and to develop techniques to approach those limits so as to maximise the achievable channel capacity. The information capacity of a linear channel with white Gaussian noise is well known and is defined by the Shannon limit. Wireless systems can approach this limit very closely - to within fractions of a dB. However, the optical channel is nonlinear. Fibre nonlinearity mixes noise with signal. Therefore, results of the linear theories on capacity can be applied in fibre channels only in the limit of very small nonlinear effects. Optical communication systems are undergoing another revolution with the development of techniques of coherent detection, the ability to detect both the amplitude and the phase of a transmitted signal and use of digital signal processing techniques to reconstruct the original signal. Use of the optical phase in emerging coherent transmission schemes opens up fundamentally new theoretical and technical possibilities most as yet unexplored. The challenge is to understand to what degree optical nonlinearity can also be compensated or, indeed, used to unlock the fibre capacity, maximise both the information transmission rate and the total bandwidth, to determine the fundamental Shannon limit for nonlinear channels and to develop methods to approach this capacity. We propose to explore fundamentally new nonlinear information technologies and to develop a practical design framework based on integration of DSP techniques, novel modulation formats, and novel source and line coding approaches tailored to the nonlinear optical channels. We believe this to be the key to designing the intelligent information infrastructure of the future.

Optical networks underpin the global digital communications infrastructure, and their development has simultaneously stimulated the growth in demand for data, and responded to this demand by unlocking the capacity of fibre-optic channels. The work within the UNLOC programme grant proved successful in understanding the fundamental limits in point-to-point nonlinear fibre channel capacity. However, the next-generation digital infrastructure needs more than raw capacity - it requires channel and flexible resource and capacity provision in combination with low latency, simplified and modular network architectures with maximum data throughput, and network resilience combined with overall network security. How to build such an intelligent and flexible network is a major problem of global importance. To cope with increasingly dynamic variations of delay-sensitive demands within the network and to enable the Internet of Skills, current optical networks overprovision capacity, resulting in both over- engineering and unutilised capacity. A key challenge is, therefore, to understand how to intelligently utilise the finite optical network resources to dynamically maximise performance, while also increasing robustness to future unknown requirements. The aim of TRANSNET is to address this challenge by creating an adaptive intelligent optical network that is able to dynamically provide capacity where and when it is needed - the backbone of the next-generation digital infrastructure. Our vision and ambition is to introduce intelligence into all levels of optical communication, cloud and data centre infrastructure and to develop optical transceivers that are optimally able to dynamically respond to varying application requirements of capacity, reach and delay. We envisage that machine learning (ML) will become ubiquitous in future optical networks, at all levels of design and operation, from digital coding, equalisation and impairment mitigation, through to monitoring, fault prediction and identification, and signal restoration, traffic pattern prediction and resource planning. TRANSNET will focus on the application of machine techniques to develop a new family of optical transceiver technologies, tailored to the needs of a new generation of self-x (x = configuring, monitoring, planning, learning, repairing and optimising) network architectures, capable of taking account of physical channel properties and high-level applications while optimising the use of resources. We will apply ML techniques to bring together the physical layer and the network; the nonlinearity of the fibres brings about a particularly complex challenge in the network context as it creates an interdependence between the signal quality of all transmitted wavelength channels. When optimising over tens of possible modulation formats, for hundreds of independent channels, over thousands of kilometres, a brute force optimisation becomes unfeasible. Particular challenges are the heterogeneity of large scale networks and the computational complexity of optimising network topology and resource allocation, as well as dynamical and data-driven management, monitoring and control of future networks, which requires a new way of thinking and tailored methodology. We propose to reduce the complexity of network design to allow self-learned network intelligence and adaptation through a combination of machine learning and probabilistic techniques. This will lead to the creation of computationally efficient approaches to deal with the complexity of the emerging nonlinear systems with memory and noise, for networks that operate dynamically on different time- and length-scales. This is a fundamentally new approach to optical network design and optimisation, requiring a cross-disciplinary approach to advance machine learning and heuristic algorithm design based on the understanding of nonlinear physics, signal processing and optical networking.

Digital-to-Analogue Conversion (DAC) that links the digital domain of '1s' and '0s' to the real-world analogue signals (current and voltage) is an indispensable functionality that enabled the modern ICT. High-speed and high-resolution of DAC, which can generate arbitrary RF signals, is the basis of various applications spanning optical communications, mobile communications, high-definition imaging and the emerging virtual reality. Nevertheless, the realisation of high-speed and high-resolution DAC is extremely challenging due to two reasons. First, there is a trade-off between the resolution (measured by the signal to noise and distortion ratio) and the speed of the DAC. Second, the conventional method of improving DAC speed by reducing the transistor size is now approaching the fundamental limit of electronic fabrication, in which the smallest transistor only contains 10s of atoms. On the other hand, photonics offer over 1000 times more bandwidth resource than conventional radio frequency (RF) electronic device. The substantial technological progress of optoelectronic component in the last decade has enabled a fine control of the amplitude and phase of a lightwave. Photodiode that converts the optical signal to electrical current now can achieve more than 100 Gigahertz frequency range. This project aims to unlock the potential of photonics technologies for future high-speed, high-resolution photonically-synthesized DAC (PhotoDAC) that is capable of generating arbitrary RF signals beyond the bounds of electronic fabrication. This capability will be enabled by a joint innovation of photonics, electronics, and digital signal processing techniques. In this project, the research team will build a prototype DAC instrument using off-the-shelf and customised components. Control software and digital signal processing schemes will be developed to ensure a durable and high-performance DAC prototype. Based on the prototype DAC instrument, the research team will investigate its application in high-speed optical communications, aiming a significantly increased transmission data rate.