Quantum error correction in crossbar architectures

A central challenge for the scaling of quantum computing systems is the need to control all qubits in the system without a large overhead. A solution for this problem in classical computing comes in the form of so called crossbar architectures. Recently we made a proposal for a large scale quantum processor~[Li et al. arXiv:1711.03807 (2017)] to be implemented in silicon quantum dots. This system features a crossbar control architecture which limits parallel single qubit control, but allows the scheme to overcome control scaling issues that form a major hurdle to large scale quantum computing systems. In this work, we develop a language that makes it possible to easily map quantum circuits to crossbar systems, taking into account their architecture and control limitations. Using this language we show how to map well known quantum error correction codes such as the planar surface and color codes in this limited control setting with only a small overhead in time. We analyze the logical error behavior of this surface code mapping for estimated experimental parameters of the crossbar system and conclude that logical error suppression to a level useful for real quantum computation is feasible.Comment: 29 + 9 pages, 13 figures, 9 tables, 8 algorithms and 3 big boxes. Comments are welcom

On Properties of Policy-Based Specifications

The advent of large-scale, complex computing systems has dramatically increased the difficulties of securing accesses to systems' resources. To ensure confidentiality and integrity, the exploitation of access control mechanisms has thus become a crucial issue in the design of modern computing systems. Among the different access control approaches proposed in the last decades, the policy-based one permits to capture, by resorting to the concept of attribute, all systems' security-relevant information and to be, at the same time, sufficiently flexible and expressive to represent the other approaches. In this paper, we move a step further to understand the effectiveness of policy-based specifications by studying how they permit to enforce traditional security properties. To support system designers in developing and maintaining policy-based specifications, we formalise also some relevant properties regarding the structure of policies. By means of a case study from the banking domain, we present real instances of such properties and outline an approach towards their automatised verification.Comment: In Proceedings WWV 2015, arXiv:1508.0338

Going Large-scale in P2P Experiments Using the JXTA Distributed Framework

The interesting properties of P2P systems (high availability despite node volatility, support for heterogeneous architectures, high scalability, etc.) make them attractive for distributed computing. However, conducting large-scale experiments with these systems arise as a major challenge. Simulation allows to model only partially the behavior of P2P prototypes. Experiments on real testbeds encounter serious difficulty with large-scale deployment and control of peers. This paper shows that using an optimized version of the JXTA Distributed Framework (JDF) allows to easily deploy, configure and control P2P experiments. We illustrate these features with sample tests performed with our JXTA-based grid data sharing service, for various large-scale configurations

Ground-state Stabilization of Open Quantum Systems by Dissipation

Control by dissipation, or environment engineering, constitutes an important methodology within quantum coherent control which was proposed to improve the robustness and scalability of quantum control systems. The system-environment coupling, often considered to be detrimental to quantum coherence, also provides the means to steer the system to desired states. This paper aims to develop the theory for engineering of the dissipation, based on a ground-state Lyapunov stability analysis of open quantum systems via a Heisenberg-picture approach. Algebraic conditions concerning the ground-state stability and scalability of quantum systems are obtained. In particular, Lyapunov stability conditions expressed as operator inequalities allow a purely algebraic treatment of the environment engineering problem, which facilitates the integration of quantum components into a large-scale quantum system and draws an explicit connection to the classical theory of vector Lyapunov functions and decomposition-aggregation methods for control of complex systems. The implications of the results in relation to dissipative quantum computing and state engineering are also discussed in this paper.Comment: 18 pages, to appear in Automatic

Challenges and trends in wireless ubiquitous computing systems

In the last decade, the Internet paradigm has been evolving toward a new frontier with the emergence of ubiquitous and pervasive systems, including wireless sensor networks, ad hoc networks, RFID systems, and wireless embedded systems. In fact, while the initial purpose of the Internet was to interconnect computers to share digital data at large scale, the current tendency is to enable ubiquitous and pervasive computing to control everything anytime and at a large scale. This new paradigm has given rise to a new generation of networked systems, commonly known as Internet-of-Things or Cyber-Physical Systems

Parallel and vector computation for stochastic optimal control applications

A general method for parallel and vector numerical solutions of stochastic dynamic programming problems is described for optimal control of general nonlinear, continuous time, multibody dynamical systems, perturbed by Poisson as well as Gaussian random white noise. Possible applications include lumped flight dynamics models for uncertain environments, such as large scale and background random atmospheric fluctuations. The numerical formulation is highly suitable for a vector multiprocessor or vectorizing supercomputer, and results exhibit high processor efficiency and numerical stability. Advanced computing techniques, data structures, and hardware help alleviate Bellman's curse of dimensionality in dynamic programming computations