Many-body models for molecular nanomagnets

We present a flexible and effective ab-initio scheme to build many-body models for molecular nanomagnets, and to calculate magnetic exchange couplings and zero-field splittings. It is based on using localized Foster-Boys orbitals as one-electron basis. We apply this scheme to three paradigmatic systems, the antiferromagnetic rings Cr8 and Cr7Ni and the single molecule magnet Fe4. In all cases we identify the essential magnetic interactions and find excellent agreement with experiments.Comment: 5 pages, 3 figure

Narrating alternatives: Story and democratic discourse in contemporary Moroccan thought (1997-2017)

El presente artículo enfoca el parámetro narrativo en relación con la construcción ideológica del discurso democrático en Marruecos entre los años 1997 y 2017. Dicho análisis se fundamenta en la teoría estructuralista de S. Chatman para el análisis narrativo y lo aplica a la deconstrucción de la narrativa ideológica en dos elementos principales: la historia como elemento objetivable y el discurso como subjetividad. Estos elementos son analizados críticamente, siguiendo la metodología del Análisis Crítico del Discurso (ACD) de T. Van Dijk en el discurso de algunos de los pensadores de referencia en Marruecos: Kamāl ‘Abd al-Latif, Ṭāhā ‘Abd al-Raḥmān (n. 1944) y Muḥammad ‘Ābid al-Ŷābrī (1935-2010)This article focuses on the narrative parameter and its relationship with the ideological construction of the discourse on democracy in Morocco between 1997 and 2017. The analysis uses S. Chatman’s structuralist theory to deconstruct the ideological narrative into two main elements: story and discourse, the former as the objective element and the latter as subjectivity. Following the CDA methodology proposed by T. Van Dijk, both story and discourse are analysed critically in relation to three important contemporary Moroccan thinkers: Kamal ‘Abd al-Latif, Ṭāhā ‘Abd al-Raḥmān (b. 1944) and Muḥammad ‘Ābid al-Ŷābrī (1935-2010)El presente trabajo se enmarca en el proyecto de I+D Ideología, texto y discurso: narrativas del cambio social en el Norte de África-IDENAF (Ref. FFI-2016-76307-R) financiado por el Plan Nacional de Investigación, Ministerio de Economía y Competitividad y los fondos FEDER de la Unión Europea, cuyo Investigador Principal es el autor. http://idenaf.hypotheses.org

Las narrativas del cambio social en el Magreb: ideología, discurso… democracia

This article is the introduction and justification of the special issue on narratives of social change in the Maghreb. It presents the main theoretical and conceptual frameworks used in the different articles in this volume. Especially relevant among them is the discussion of the place of discourse in the theoretical framework of Post-orientalism developed by Hamid Dabashi (2009, 2012) and in Post-colonial studies. In this regard, the relationship between ideology and discourse (Van Dijk, 2011) is introduced and discussed in connection with the concept of social change. Social change is understood as a broad narrative comprised of a diverse textuality that belongs to areas such as intellectual discourse, literature and jurisprudence, and includes the gender perspectiveEste artículo constituye la introducción y justificación al volumen monográfico sobre narrativas de cambio social en el Magreb, presentando las principales pautas teóricas y conceptuales que siguen los diferentes artículos incluidos en el mismo. Entre ellas, destaca la reflexión conjunta sobre el lugar del discurso en el marco teórico del post-orientalismo propuesto por Hamid Dabashi (2009, 2012) y los estudios post-coloniales. En este sentido, se introduce la relación entre ideología y discurso (Van Dijk, 2011) y se relaciona con el concepto de cambio social, entendido como una narrativa amplia que se desglosa en una textualidad diversa que pertenece a áreas como el discurso intelectual, la literatura o la jurisprudenciaEl presente trabajo se enmarca en el proyecto de I+D Ideología, texto y discurso: narrativas del cambio social en el Norte de África-IDENAF (Ref. FFI-2016-76307-R) financiado por el Plan Nacional de Investigación, Ministerio de Economía y Competitividad y los fondos FEDER de la Unión Europea, cuyo Investigador Principal es el autor. http://idenaf.hypotheses.org

End-to-End Entanglement Generation Strategies: Capacity Bounds and Impact on Quantum Key Distribution

A first quantum revolution has already brought quantum technologies into our everyday life for decades: in fact, electronics and optics are based on the quantum mechanical principles. Today, a second quantum revolution is underway, leveraging the quantum principles of superposition, entanglement and measurement, which were not fully exploited yet. International innovation activities and standardization bodies have identified four main application areas for quantum technologies and services: quantum secure communications, quantum computing, quantum simulation, and quantum sensing and metrology. This paper focuses on quantum secure communications by addressing the evolution of Quantum Key Distribution (QKD) networks (under early exploitation today) towards the Quantum-ready networks and the Quantum Internet based also on entanglement distribution. Assuming that management and control of quantum nodes is a key challenge under definition, today, a main obstacle in exploiting long-range QKD and Quantum-ready networks concerns the inherent losses due to the optical transmission channels. Currently, it is assumed that a most promising way for overcoming this limitation, while avoiding the presence of costly trusted nodes, it is to distribute entangled states by means of Quantum Repeaters. In this respect, the paper provides an overview of current methods and systems for end-to-end entanglement generation, with some simulations and a discussion of capacity upper bounds and their impact of secret key rate in QKD systems

A holographic perspective on phonons and pseudo-phonons

We analyze the concomitant spontaneous breaking of translation and conformal symmetries by introducing in a CFT a complex scalar operator that acquires a spatially dependent expectation value. The model, inspired by the holographic Q-lattice, provides a privileged setup to study the emergence of phonons from a spontaneous translational symmetry breaking in a conformal field theory and offers valuable hints for the treatment of phonons in QFT at large. We first analyze the Ward identity structure by means of standard QFT techniques, considering both spontaneous and explicit symmetry breaking. Next, by implementing holographic renormalization, we show that the same set of Ward identities holds in the holographic Q-lattice. Eventually, relying on the holographic and QFT results, we study the correlators realizing the symmetry breaking pattern and how they encode information about the low-energy spectrum.Comment: 31+1 pages, version accepted on JHE

The nahda as a political awakening in the Maghreb: historical and conceptual tensions in Mālik Bennabī’s thought

La figura del pensador argelino Mālik Bennabī (1905-1973) es sin duda una de las más importantes e influyentes del pensamiento magrebí y árabe contemporáneo. Partiendo de una lectura salafí y nacionalista, el islam es considerado por Bennabī como una herramienta de liberación cultural y política de los pueblos colonizados del Tercer Mundo. Su conceptuación ideológica procede de la salafiyya, por una parte, y del pensamiento nacionalista europeo, por otra, y es analizada en el presente artículo a partir del concepto de “nahda”, el cual constituye uno de los vértices metodológicos y conceptuales de su pensamiento político. Dicho concepto, además, pone en relación el pensamiento político anticolonialista árabe con la realidad sociopolítica de los países árabes en la actualidad.The Algerian thinker Mālik Bennabī (1905-1973) is one of the most important and influent figures of Contemporary Maghrebi and Arab thought. Starting from a wide salafi and nationalistic view, Islam is considered by Bennabī as a cultural and political liberation tool in the colonized areas of the Third World. His ideological conceptualization comes from the salafiyya, as well as from the European nationalistic thought, and in this article it is analysed through the concept of “nahda”, which is one of the methodological and conceptual keywords in his political thought. This concept links also the anticolonialist Arab political thought to the socio-political facts in the nowadays Arab countries

Enhancement of rare-earth--transition-metal exchange interaction in Pr2_{2}Fe17_{17} probed by inelastic neutron scattering

The fundamental magnetic interactions of Pr$_{2}$Fe$_{17}$ are studied by inelastic neutron scattering and anisotropy field measurements. Data analysis confirms the presence of three magnetically inequivalent sites, and reveals an exceptionally large value of the exchange field. The unexpected importance of $J$-mixing effects in the description of the ground-state properties of Pr$_{2}$Fe$_{17}$ is evidenced, and possible applications of related compounds are envisaged.Comment: 4 RevTeX pages, 4 EPS figures. Accepted for publication by Appl. Phys. Lett. (will be found at http://apl.aip.org

S-mixing and quantum tunneling of the magnetization in molecular nanomagnets

The role of $S$-mixing in the quantum tunneling of the magnetization in nanomagnets has been investigated. We show that the effect on the tunneling frequency is huge and that the discrepancy (more than 3 orders of magnitude in the tunneling frequency) between spectroscopic and relaxation measurements in Fe$_8$ can be resolved if $S$-mixing is taken into account.Comment: REVTEX, 10 pages, 3 jpg figures, to appear in PR

The First Cold Antihydrogen

Antihydrogen, the atomic bound state of an antiproton and a positron, was produced at low energy for the first time by the ATHENA experiment, marking an important first step for precision studies of atomic antimatter. This paper describes the first production and some subsequent developments.Comment: Invitated Talk at COOL03, International Workshop on Beam Cooling and Related Topics, to be published in NIM