Non-classical computing: feasible versus infeasible

Physics sets certain limits on what is and is not computable. These limits are very far from having been reached by current technologies. Whilst proposals for hypercomputation are almost certainly infeasible, there are a number of non classical approaches that do hold considerable promise. There are a range of possible architectures that could be implemented on silicon that are distinctly different from the von Neumann model. Beyond this, quantum simulators, which are the quantum equivalent of analogue computers, may be constructable in the near future

International White Book on DER Protection : Review and Testing Procedures

This white book provides an insight into the issues surrounding the impact of increasing levels of DER on the generator and network protection and the resulting necessary improvements in protection testing practices. Particular focus is placed on ever increasing inverter-interfaced DER installations and the challenges of utility network integration. This white book should also serve as a starting point for specifying DER protection testing requirements and procedures. A comprehensive review of international DER protection practices, standards and recommendations is presented. This is accompanied by the identifi cation of the main performance challenges related to these protection schemes under varied network operational conditions and the nature of DER generator and interface technologies. Emphasis is placed on the importance of dynamic testing that can only be delivered through laboratory-based platforms such as real-time simulators, integrated substation automation infrastructure and fl exible, inverter-equipped testing microgrids. To this end, the combination of fl exible network operation and new DER technologies underlines the importance of utilising the laboratory testing facilities available within the DERlab Network of Excellence. This not only informs the shaping of new protection testing and network integration practices by end users but also enables the process of de-risking new DER protection technologies. In order to support the issues discussed in the white paper, a comparative case study between UK and German DER protection and scheme testing practices is presented. This also highlights the level of complexity associated with standardisation and approval mechanisms adopted by different countries

What is a quantum simulator?

Quantum simulators are devices that actively use quantum effects to answer questions about model systems and, through them, real systems. Here we expand on this definition by answering several fundamental questions about the nature and use of quantum simulators. Our answers address two important areas. First, the difference between an operation termed simulation and another termed computation. This distinction is related to the purpose of an operation, as well as our confidence in and expectation of its accuracy. Second, the threshold between quantum and classical simulations. Throughout, we provide a perspective on the achievements and directions of the field of quantum simulation.Comment: 13 pages, 2 figure

European White Book on Real-Time Power Hardware in the Loop Testing : DERlab Report No. R- 005.0

The European White Book on Real-Time-Powerhardware-in-the-Loop testing is intended to serve as a reference document on the future of testing of electrical power equipment, with specifi c focus on the emerging hardware-in-the-loop activities and application thereof within testing facilities and procedures. It will provide an outlook of how this powerful tool can be utilised to support the development, testing and validation of specifi cally DER equipment. It aims to report on international experience gained thus far and provides case studies on developments and specifi c technical issues, such as the hardware/software interface. This white book compliments the already existing series of DERlab European white books, covering topics such as grid-inverters and grid-connected storag

From Quantum Optics to Quantum Technologies

Quantum optics is the study of the intrinsically quantum properties of light. During the second part of the 20th century experimental and theoretical progress developed together; nowadays quantum optics provides a testbed of many fundamental aspects of quantum mechanics such as coherence and quantum entanglement. Quantum optics helped trigger, both directly and indirectly, the birth of quantum technologies, whose aim is to harness non-classical quantum effects in applications from quantum key distribution to quantum computing. Quantum light remains at the heart of many of the most promising and potentially transformative quantum technologies. In this review, we celebrate the work of Sir Peter Knight and present an overview of the development of quantum optics and its impact on quantum technologies research. We describe the core theoretical tools developed to express and study the quantum properties of light, the key experimental approaches used to control, manipulate and measure such properties and their application in quantum simulation, and quantum computing.Comment: 20 pages, 3 figures, Accepted, Prog. Quant. Ele

Exploring quantum many-body systems from the viewpoints of quantum computing and spectroscopy

Understanding quantum many-body behaviours such as exotic phases and spectroscopic properties in quantum materials and molecular systems is a long-standing problem of both fundamental and practical interest in quantum physics. This understanding provides insights into the true underlying physics of quantum many-body systems, aids in the prediction of the microscopic and macroscopic properties of those systems, and also advances the rational design and synthesis of novel materials. However, our ability to understand quantum many-body behaviours has hitherto been limited, due to the excessive demands imposed on classical computing by the inherent complexity of describing and analysing those behaviours. While the advent of quantum computing has opened up new possibilities for examining these questions, the current generation of quantum technology does not yet present a feasible, standalone way to solve the above problem. However, a fusion of classical and quantum approaches could arguably provide a viable way of exploring interesting quantum phenomena. The central objective of this thesis is to achieve such a synthesis in practice, and to establish a corresponding framework for the study of quantum many-body systems. One area of particular interest is the intersection between quantum computing and spectroscopy, specifically in terms of the latter's potential to greatly assist in the investigation of quantum many-body phenomena. Quantum many-body problems in general can be divided into two classes, static and dynamic problems, which correspond to the estimation of eigenstate properties (such as eigenenergies and order parameters in different phases), and dynamical properties (such as response to an external field). In Part II, I present a number of approaches to solve these static and dynamic problems. I initially establish a quantum computing framework based on hybrid quantum-classical tensor networks, which incorporate the inherent advantages of classical tensor networks and quantum computing to represent the quantum system. I then demonstrate how eigenstate properties can be estimated by a randomised linear-combination-of-unitary method, termed algorithmic cooling, with at most one ancillary qubit; this achieves a logarithmic circuit complexity with respect to precision in eigenstate property estimation, and reaches the Heisenberg limit in eigenenergy estimation. Turning to dynamic problems, I present an adaptive product formula approach to construct a low-depth quantum circuit for simulating quantum dynamics. I further show how to enable large-scale dynamics simulation based on hybrid tensor networks, followed by a perturbative approach to simulating quantum many-body dynamics. In Part III, I first demonstrate how spectroscopic features of quantum systems can be probed. Equipped with the framework and methods established and developed in this thesis, I study quantum many-body phenomena, and excitation spectra in interacting bosons, fermions, and quantum spins through numerics and experiments. In Part IV, the quantum resources required for the application of quantum computing to realistic problems in the near future are assessed, together with the challenges that accompany such application. This encompasses a discussion of the estimated resources needed for estimating eigenstate properties of spins, fermions and molecules, in respect of both noisy quantum processors and fault-tolerant quantum computers. I then address some of the inherent challenges of using near-term noisy quantum devices, such as encountering unavoidable quantum process errors and statistical errors, by applying error mitigation, and efficient grouping measurement schemes proposed in this thesis. Finally, I conclude with a few remarks on the development of quantum computing in solving quantum many-body systems, and I pose outlooks for further research in this field

Modelling and Co-simulation of Multi-Energy Systems: Distributed Software Methods and Platforms

L'abstract è presente nell'allegato / the abstract is in the attachmen

Simulating chemistry using quantum computers

The difficulty of simulating quantum systems, well-known to quantum chemists, prompted the idea of quantum computation. One can avoid the steep scaling associated with the exact simulation of increasingly large quantum systems on conventional computers, by mapping the quantum system to another, more controllable one. In this review, we discuss to what extent the ideas in quantum computation, now a well-established field, have been applied to chemical problems. We describe algorithms that achieve significant advantages for the electronic-structure problem, the simulation of chemical dynamics, protein folding, and other tasks. Although theory is still ahead of experiment, we outline recent advances that have led to the first chemical calculations on small quantum information processors.Comment: 27 pages. Submitted to Ann. Rev. Phys. Che

Going Beyond Gadgets: The Importance of Scalability for Analogue Quantum Simulators

We propose a theoretical framework for analogue quantum simulation to capture the full scope of experimentally realisable simulators, motivated by a set of fundamental criteria first introduced by Cirac and Zoller. Our framework is consistent with Hamiltonian encodings used in complexity theory, is stable under noise, and encompasses a range of possibilities for experiment, such as the simulation of open quantum systems and overhead reduction using Lieb-Robinson bounds. We discuss the requirement of scalability in analogue quantum simulation, and in particular argue that simulation should not involve interaction strengths that grow with the size of the system. We develop a general framework for gadgets used in Hamiltonian complexity theory, which may be of interest independently of analogue simulation, and in particular prove that size-dependent scalings are unavoidable in Hamiltonian locality reduction. However, if one allows for an additional resource of engineered dissipation, we demonstrate a scheme that circumvents the locality reduction no-go theorem using the quantum Zeno effect. Our gadget framework opens the door to formalise and resolve long-standing open questions about gadgets. We conclude with a discussion on universality results in analogue quantum simulation.Comment: 52 pages, 12 figures; revised proof of proposition 16 and slightly strengthened result, typos corrected, references added, minor edits to abstract and main tex