A Silicon Surface Code Architecture Resilient Against Leakage Errors

Spin qubits in silicon quantum dots are one of the most promising building blocks for large scale quantum computers thanks to their high qubit density and compatibility with the existing semiconductor technologies. High fidelity single-qubit gates exceeding the threshold of error correction codes like the surface code have been demonstrated, while two-qubit gates have reached 98\% fidelity and are improving rapidly. However, there are other types of error --- such as charge leakage and propagation --- that may occur in quantum dot arrays and which cannot be corrected by quantum error correction codes, making them potentially damaging even when their probability is small. We propose a surface code architecture for silicon quantum dot spin qubits that is robust against leakage errors by incorporating multi-electron mediator dots. Charge leakage in the qubit dots is transferred to the mediator dots via charge relaxation processes and then removed using charge reservoirs attached to the mediators. A stabiliser-check cycle, optimised for our hardware, then removes the correlations between the residual physical errors. Through simulations we obtain the surface code threshold for the charge leakage errors and show that in our architecture the damage due to charge leakage errors is reduced to a similar level to that of the usual depolarising gate noise. Spin leakage errors in our architecture are constrained to only ancilla qubits and can be removed during quantum error correction via reinitialisations of ancillae, which ensure the robustness of our architecture against spin leakage as well. Our use of an elongated mediator dots creates spaces throughout the quantum dot array for charge reservoirs, measuring devices and control gates, providing the scalability in the design

Integrating security and usability into the requirements and design process

According to Ross Anderson, 'Many systems fail because their designers protect the wrong things or protect the right things in the wrong way'. Surveys also show that security incidents in industry are rising, which highlights the difficulty of designing good security. Some recent approaches have targeted security from the technological perspective, others from the human–computer interaction angle, offering better User Interfaces (UIs) for improved usability of security mechanisms. However, usability issues also extend beyond the user interface and should be considered during system requirements and design. In this paper, we describe Appropriate and Effective Guidance for Information Security (AEGIS), a methodology for the development of secure and usable systems. AEGIS defines a development process and a UML meta-model of the definition and the reasoning over the system's assets. AEGIS has been applied to case studies in the area of Grid computing and we report on one of these

Supporting Complex Scientific Database Schemas in a Grid Middleware

“This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder." “Copyright IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.” DOI: 10.1109/AINA.2009.129The volume of digital scientific data has increased considerably with advancing technologies of computing devices and scientific instruments. We are exploring the use of emerging Grid technologies for the management and manipulation of very large distributed scientific datasets. Taking as an example a terabyte-size scientific database with complex database schema, this paper focuses on the potential of a well-known Grid middleware - OGSA-DQP - for distributing such datasets. In particular, we investigate and extend the data type support in this system to handle a complex schema of a real scientific database - the Sloan Digital Sky Survey database

Modular System for Shelves and Coasts (MOSSCO v1.0) - a flexible and multi-component framework for coupled coastal ocean ecosystem modelling

Shelf and coastal sea processes extend from the atmosphere through the water column and into the sea bed. These processes are driven by physical, chemical, and biological interactions at local scales, and they are influenced by transport and cross strong spatial gradients. The linkages between domains and many different processes are not adequately described in current model systems. Their limited integration level in part reflects lacking modularity and flexibility; this shortcoming hinders the exchange of data and model components and has historically imposed supremacy of specific physical driver models. We here present the Modular System for Shelves and Coasts (MOSSCO, http://www.mossco.de), a novel domain and process coupling system tailored---but not limited--- to the coupling challenges of and applications in the coastal ocean. MOSSCO builds on the existing coupling technology Earth System Modeling Framework and on the Framework for Aquatic Biogeochemical Models, thereby creating a unique level of modularity in both domain and process coupling; the new framework adds rich metadata, flexible scheduling, configurations that allow several tens of models to be coupled, and tested setups for coastal coupled applications. That way, MOSSCO addresses the technology needs of a growing marine coastal Earth System community that encompasses very different disciplines, numerical tools, and research questions.Comment: 30 pages, 6 figures, submitted to Geoscientific Model Development Discussion

Simulator Development - Annual Report Year 2

In this paper the simulation environment for the CATNETS project is defined further. The chosen simulator is adopted in terms of new features an architecture changes in order to provide a valid simulation environment for Application Layer Network scenarios. Furthermore the requirements for a scenario generator and the needed configuration mechanisms for the actual simulation runs are introduced. --Grid Computing

Mediation Patterns for Message Exchange Protocols

Systems interact with their environment (e.g., other systems) by ex-changing messages in a particular order. Interoperability problems arise when systems do not understand each other’s messages or follow incompatible message exchange protocols. In this paper we identify mismatches in message ex-change protocols (involving two systems) and we propose solution patterns to compensate these mismatches

Leveraging legacy codes to distributed problem solving environments: A web service approach

This paper describes techniques used to leverage high performance legacy codes as CORBA components to a distributed problem solving environment. It first briefly introduces the software architecture adopted by the environment. Then it presents a CORBA oriented wrapper generator (COWG) which can be used to automatically wrap high performance legacy codes as CORBA components. Two legacy codes have been wrapped with COWG. One is an MPI-based molecular dynamic simulation (MDS) code, the other is a finite element based computational fluid dynamics (CFD) code for simulating incompressible Navier-Stokes flows. Performance comparisons between runs of the MDS CORBA component and the original MDS legacy code on a cluster of workstations and on a parallel computer are also presented. Wrapped as CORBA components, these legacy codes can be reused in a distributed computing environment. The first case shows that high performance can be maintained with the wrapped MDS component. The second case shows that a Web user can submit a task to the wrapped CFD component through a Web page without knowing the exact implementation of the component. In this way, a user’s desktop computing environment can be extended to a high performance computing environment using a cluster of workstations or a parallel computer