José Ramón Portillo

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Graphical features on map, charts, diagrams and graph drawings usually must be annotated with text labels in order to convey their meaning. In this paper we focus on a problem that arises when labeling schematized maps, e.g. for subway networks. We present algorithms for labeling points on a line with axis-parallel rectangular labels of equal height. Our(More)
We show how to prepare any graph state of up to 12 qubits with: (a) the minimum number of controlled-Z gates, and (b) the minimum preparation depth. We assume only one-qubit and controlled-Z gates. The method exploits the fact that any graph state belongs to an equivalence class under local Clifford operations. We extend up to 12 qubits the classification(More)
Quantum correlations are contextual yet, in general, nothing prevents the existence of even more contextual correlations. We identify and test a noncontextuality inequality in which the quantum violation cannot be improved by any hypothetical postquantum theory, and use it to experimentally obtain correlations in which the fraction of noncontextual(More)
Recently, several inequalities involving sequences of measurements have been proposed which hold for non-contextual models but which are violated in quantum mechanics. They also have been found to be violated in experiments and the violation is independent of the prepared quantum state. A typical contextual model explaining this violation uses a classical(More)
The following problem of rectilinear routing is NP-complete: Given pairs of points on a surface whether it is possible choosen an orthogonal path with only one bend for each, avoiding all intersections. For particular surfaces like cylinder or torus, that question still are an open problem. Focusing on a cylinder, we conjecture about it solvability in(More)
Adán Cabello, 2 Lars Eirik Danielsen, Antonio J. López-Tarrida, and José R. Portillo Departamento de F́ısica Aplicada II, Universidad de Sevilla, E-41012 Sevilla, Spain Department of Physics, Stockholm University, S-10691 Stockholm, Sweden Department of Informatics, University of Bergen, P.O. Box 7803, N-5020 Bergen, Norway Departamento de Matemática(More)
We study problems that arise in the context of covering certain geometric objects (so-called seeds, e.g., points or disks) by a set of other geometric objects (a so-called cover, e.g., a set of disks or homothetic triangles). We insist that the interiors of the seeds and the cover elements are pairwise disjoint, but they can touch. We call the contact graph(More)