87 research outputs found

    Quantum measurements with prescribed symmetry

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    We introduce a method to determine whether a given generalised quantum measurement is isolated or it belongs to a family of measurements having the same prescribed symmetry. The technique proposed reduces to solving a linear system of equations in some relevant cases. As consequence, we provide a simple derivation of the maximal family of Symmetric Informationally Complete measurements (SIC)-POVM in dimension 3. Furthermore, we show that the following remarkable geometrical structures are isolated, so that free parameters cannot be introduced: (a) maximal sets of mutually unbiased bases in prime power dimensions from 4 to 16, (b) SIC-POVM in dimensions from 4 to 16 and (c) contextuality Kochen-Specker sets in dimension 3, 4 and 6, composed of 13, 18 and 21 vectors, respectively.Comment: 10 pages, 2 figure

    Quantum mechanics in finite dimensional Hilbert space

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    The quantum mechanical formalism for position and momentum of a particle in a one dimensional cyclic lattice is constructively developed. Some mathematical features characteristic of the finite dimensional Hilbert space are compared with the infinite dimensional case. The construction of an unbiased basis for state determination is discussed.Comment: 14 pages, no figure

    V√°stago recubierto de hidroxiapatita: Revisi√≥n a 5 a√Īos

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    Se eval√ļan los resultados cl√≠nicos y radiol√≥gicos de 65 v√°stagos femorales recubiertos proximalmente de hidroxiapatita de m√°s de 5 a√Īos y la existencia de una clara correlaci√≥n de los cambios remodelativos con los patrones de estr√©s estudiados por elementos finitos. La edad media fue de 56 a√Īos y la patolog√≠a preoperativa m√°s frecuente fue la artrosis en 38 caos, seguida de la necrosis as√©ptica en 15. Se utiliz√≥ el protocolo de Johnston y col. y el baremo num√©rico de Merle D'Aubign√©, pasando sobre 18 en la revisi√≥n. En el 98,4% no hab√≠a dolor o era ligero y ocasional. Radiogr√°ficamente se vieron l√≠neas radiol√ļcidas alrededor de la parte distal del v√°stago pulida y afilada en el 89,2%, no apareciendo en las zonas recubiertas de hidroxiapatita. Apareci√≥ hipertrofia cortical reactiva en el 13,8% y peque√Īas im√°genes de oste√≥lisis a nivel proximal en el 10,8 %. Seg√ļn los criterios de Neg. el 100% de los v√°stagos estaban osteointegrados.The clinical and radiological results of 65 proximally HA-coated femoral stems were assessed after a minimum follow-up period of five years. The relationship between remodelative changes and the stress patterns was clearly disclosed by finite element modelling. Mean age was 56 years. The most common etiology was osteoarthritis in 38 cases and vascular necrosis in 15. Radiographic and clinical assessment was done after Johnston and col's protocol and the numeric rating of Merle D'Aubigne respectively. The mean preoperative score was 8,5 points, becoming 17,4 points out of 18 at the 5 years review. Occasional or absent pain was fount in 98% of the cases. There were radiolucency lines surrounding the polished and sharp distal stem in 89%, but they were not present at the HA-coated zones. Reactive cortical hypertrophy was present in 14 % and proximal small osteolytics features in 11%. According Engh's criteria, the 100% of the stems were osteintegrated

    Entanglement for all quantum states

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    It is shown that a state that is factorizable in the Hilbert space corresponding to some choice of degrees of freedom, becomes entangled for a different choice of degrees of freedom. Therefore, entanglement is not a special case but is ubiquitous in quantum systems. Simple examples are calculated and a general proof is provided. The physical relevance of the change of tensor product structure is mentioned.Comment: 9 page

    Quantum diffusion on a cyclic one dimensional lattice

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    The quantum diffusion of a particle in an initially localized state on a cyclic lattice with N sites is studied. Diffusion and reconstruction time are calculated. Strong differences are found for even or odd number of sites and the limit N->infinit is studied. The predictions of the model could be tested with micro - and nanotechnology devices.Comment: 17 pages, 5 figure
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