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We describe Pad++, a zoomable graphical sketchpad that we are exploring as an alternative to traditional window and icon-based interfaces. We discuss the motivation for Pad++, describe the implementation, and present prototype applications. In addition, we introduce an informational physics strategy for interface design and briefly contrast it with current(More)
A general scheme to perform universal, fault-tolerant quantum computation within decoherence-free subspaces (DFSs) is presented. At most two-qubit interactions are required, and the system remains within the DFS throughout the entire implementation of a quantum gate. We show explicitly how to perform universal computation on clusters of the four-qubit DFS(More)
An operator sum representation is derived for a decoherence-free subspace (DFS) and used to (i) show that DFSs are the class of quantum error correcting codes (QECCs) with fixed, unitary recovery operators, and (ii) find explicit representations for the Kraus operators of collective decoherence. We demonstrate how this can be used to construct a(More)
This thesis develops restrictions governing how a quantum system, jointly held by two parties, can be altered by the local actions of those parties, under assumptions about how they may communicate. These restrictions are expressed as constraints involving the eigenvalues of the density matrix of one of the parties. The thesis is divided into two parts.(More)
Preserving the coherence of quantum states and controlling their unitary evolution is one of the fundamental goals of Quantum Information Processing [1]. When the system Hamiltonian is invariant under particle permutations, the exchange operator Eij interchanging particles i and j is a constant of the motion, and definite symmetry of a state will be(More)
The eagerly awaited SOAP (Sepsis Occurrence in Acutely ill Patients) study is published and its observational data provide much of interest, not least in generating further hypotheses on improving treatment in this challenging group. Glycaemic control in the critically ill is once more the focus of attention, and we discuss three studies in this area. Not(More)
Andrew Staniforth described an international community effort in the verification of mesoscale models--the COMPARE (Comparison of Model Prediction and Research Experiments) Project under the auspices of the CAS/JSC Working Group on Numerical Experimentation. Recherche en Prevision Numerique of Environment Canada has taken the lead in this effort. The idea(More)