Quantum MERA Channels

Tensor networks representations of many-body quantum systems can be described in terms of quantum channels. We focus on channels associated with the Multi-scale Entanglement Renormalization Ansatz (MERA) tensor network that has been recently introduced to efficiently describe critical systems. Our approach allows us to compute the MERA correspondent to the thermodynamic limit of a critical system introducing a transfer matrix formalism, and to relate the system critical exponents to the convergence rates of the associated channels.Comment: 4 pages, 2 figure

A fingerprint biometric cryptosystem in FPGA

Comunicación presentada al ICIT 2015 celebrado en Sevilla del 17 al 19 de marzo de 2015This paper presents the implementation of a complete fingerprint biometric cryptosystem in a Field Programmable Gate Array (FPGA). This is possible thanks to the use of a novel fingerprint feature, named QFingerMap, which is binary, length-fixed, and ordered. Security of Authentication on FPGA is further improved because information stored is protected due to the design of a cryptosystem based on Fuzzy Commitment. Several samples of fingers as well as passwords can be fused at feature level with codewords of an error correcting code to generate non-sensitive data. System performance is illustrated with experimental results corresponding to 560 fingerprints acquired in live by an optical sensor and processed by the system in a Xilinx Virtex 6 FPGA. Depending on the realization, more or less accuracy is obtained, being possible a perfect authentication (zero Equal Error Rate), with the advantages of real-time operation, low power consumption, and a very small devicePeer reviewe

Crossed Andreev reflection-induced magnetoresistance

We show that very large negative magnetoresistance can be obtained in magnetic trilayers in a current-in-plane geometry owing to the existence of crossed Andreev reflection. This spin-valve consists of a thin superconducting film sandwiched between two ferromagnetic layers whose magnetization is allowed to be either parallelly or antiparallelly aligned. For a suitable choice of structure parameters and nearly fully spin-polarized ferromagnets the magnetoresistance can exceed -80%. Our results are relevant for the design and implementation of spintronic devices exploiting ferromagnet-superconductor structures.Comment: 5 pages, 4 figures, final published versio

Adiabatic pumping through interacting quantum dots

We present a general formalism to study adiabatic pumping through interacting quantum dots. We derive a formula that relates the pumped charge to the local, instantaneous Green function of the dot. This formula is then applied to the infinite-U Anderson model both for weak and strong tunnel-coupling strengths.Comment: 4 pages, 3 figure

Subjetividad y educabilidad: orientaciones para la praxis docente

Durante los últimos diez años Peiró estuvo en universidades iberoamericanas explicando, como ponente, gestor de cursos, investigando... El tema expone los hallazgos de nuestras investigaciones sobre incivilidad escolar: enseñar valores, desarrollar el autocontrol de emociones, evitar actitudes violentas, etc. El núcleo sobre el que actuar es la subjetividad de los escolares, que aquí desglosamos. Todo esto se expone confrontando legislación y obras de autores de prestigio. Esto trae que debamos profundizar en el estudio del educando, integrando las aportaciones de las neurociencias y demás materias antropológicas, con el fin de reinterpretar la educabilidad como algo más que mera ductilidad, sin desprenderse de lo intelectual, afectivo y conductual interactivamente.The theme describes the roots of teaching values to prevent mispeaceful coexistence, develop self-control of emotions, etc. interrelated whole. The nucleus on which to act is the subjectivity of the school, that is analyzed. This is laid out facing the law and articles of leading authors. This brings that we should further study the learner, integrating contributions from neuroscience and anthropology themes, in order to reinterpret the educability as more than mere ductility, without abandoning the intellectual, emotional and behavioral interactivity

Fin de las diplomaturas de magisterio: Motivaciones, dificultad y satisfacción con la formación de sus últimos alumnos

Este artículo presenta un estudio realizado en dos universidades españolas poco antes de la implantación de los grados de magisterio adaptados al Espacio Europeo de Educación Superior (EEES). Se han analizado las opiniones de los alumnos de cinco especialidades con el objetivo de conocer sus opiniones sobre sus motivaciones para matricularse en una determinada especialidad, la dificultad de la titulación y el grado de satisfacción con la formación recibida. Además de los resultados y conclusiones obtenidas, esta investigación pretende servir de referencia para aquellos investigadores que, en un futuro, analicen qué ha supuesto la desaparición de la mayor parte de las especialidades de magisterio y la adaptación al marco fijado por el EEE

Andreev interference in adiabatic pumping

Within the scattering approach, we develop a model for adiabatic quantum pumping in hybrid normal/superconductor systems where several superconducting leads are present. This is exploited to study Andreev-interference effects on adiabatically pumped charge in a 3-arm beam splitter attached to one normal and two superconducting leads with different phases of the order parameters. We derive expressions for the pumped charge through the normal lead for different parameters for the scattering region, and elucidate the effects due to Andreev interference. In contrast to what happens for voltage-driven transport, Andreev interference does not yield in general a pumped current which is a symmetric function of the superconducting-phase difference.Comment: 4 pages, 1 figur

Microelectronics implementation of directional image-based fuzzy templates for fingerprints

Trabajo presentado al ICM celebrado en El Cairo del 19 al 22 de diciembre de 2010.Fingerprint orientation image, also called directional image, is a widely used method in fingerprint recognition. It helps in classification (accelerating fingerprint identification process) as well as in preprocessing or processing steps (such as fingerprint enhancement or minutiae extraction). Hence, efficient storage of directional image-based information is relevant to achieve low-cost templates not only for “match on card” but also for “authentication on card” solutions. This paper describes how to obtain a fuzzy model to describe the directional image of a fingerprint and how this model can be implemented in hardware efficiently. The CAD tools of the Xfuzzy 3 environment have been employed to accelerate the fuzzy modeling process as well as to implement the directional image-based template into both an FPGA from Xilinx and an ASIC.Peer Reviewe

Decoherence induced by interacting quantum spin baths

We study decoherence induced on a two-level system coupled to a one-dimensional quantum spin chain. We consider the cases where the dynamics of the chain is determined by the Ising, XY, or Heisenberg exchange Hamiltonian. This model of quantum baths can be of fundamental importance for the understanding of decoherence in open quantum systems, since it can be experimentally engineered by using atoms in optical lattices. As an example, here we show how to implement a pure dephasing model for a qubit system coupled to an interacting spin bath. We provide results that go beyond the case of a central spin coupled uniformly to all the spins of the bath, in particular showing what happens when the bath enters different phases, or becomes critical; we also study the dependence of the coherence loss on the number of bath spins to which the system is coupled and we describe a coupling-independent regime in which decoherence exhibits universal features, irrespective of the system-environment coupling strength. Finally, we establish a relation between decoherence and entanglement inside the bath. For the Ising and the XY models we are able to give an exact expression for the decay of coherences, while for the Heisenberg bath we resort to the numerical time-dependent Density Matrix Renormalization Group.Comment: 18 pages, 20 figure