Entanglement from density measurements: analytical density-functional for the entanglement of strongly correlated fermions

We derive an analytical density functional for the single-site entanglement of the one-dimensional homogeneous Hubbard model, by means of an approximation to the linear entropy. We show that this very simple density functional reproduces quantitatively the exact results. We then use this functional as input for a local density approximation to the single-site entanglement of inhomogeneous systems. We illustrate the power of this approach in a harmonically confined system, which could simulate recent experiments with ultracold atoms in optical lattices as well as in a superlattice and in an impurity system. The impressive quantitative agreement with numerical calculations -- which includes reproducing subtle signatures of the particle density stages -- shows that our density-functional can provide entanglement calculations for actual experiments via density measurements. Next we use our functional to calculate the entanglement in disordered systems. We find that, at contrast with the expectation that disorder destroys the entanglement, there exist regimes for which the entanglement remains almost unaffected by the presence of disordered impurities.Comment: 6 pages, 3 figure

Feasibility of approximating spatial and local entanglement in long-range interacting systems using the extended Hubbard model

We investigate the extended Hubbard model as an approximation to the local and spatial entanglement of a one-dimensional chain of nanostructures where the particles interact via a long range interaction represented by a `soft' Coulomb potential. In the process we design a protocol to calculate the particle-particle spatial entanglement for the Hubbard model and show that, in striking contrast with the loss of spatial degrees of freedom, the predictions are reasonably accurate. We also compare results for the local entanglement with previous results found using a contact interaction (PRA, 81 (2010) 052321) and show that while the extended Hubbard model recovers a better agreement with the entanglement of a long-range interacting system, there remain realistic parameter regions where it fails to predict the quantitative and qualitative behaviour of the entanglement in the nanostructure system.Comment: 6 pages, 5 figures and 1 table; added results with correlated hopping term; accepted by EP

Hubbard model as an approximation to the entanglement in nanostructures

We investigate how well the one-dimensional Hubbard model describes the entanglement of particles trapped in a string of quantum wells. We calculate the average single-site entanglement for two particles interacting via a contact interaction and consider the effect of varying the interaction strength and the interwell distance. We compare the results with the ones obtained within the one-dimensional Hubbard model with on-site interaction. We suggest an upper bound for the average single-site entanglement for two electrons in M wells and discuss analytical limits for very large repulsive and attractive interactions. We investigate how the interplay between interaction and potential shape in the quantum-well system dictates the position and size of the entanglement maxima and the agreement with the theoretical limits. Finally, we calculate the spatial entanglement for the quantum-well system and compare it to its average single-site entanglement

Verses, subverses and subversions in contemporary postcolonial poetry : the arts of resistance in the works of Linton Kwesi Johnson and Lesego Rampolokeng

Includes bibliographical references (leaves 136-141).This dissertation seeks to analyse insubordination and resistance manifested in postcolonial and post-apartheid poetry as ways of subverting dominant Western discourses. More specifically, I focus my analysis on textual strategies of resistance in the poetry of Linton Kwesi Johnson and Lesego Rampolokeng. The syncretistic quality in the oeuvres of both poets is related to diaspora, hybridity and crealisation as forms of writ[h]ing against (neo)colonially-based hegemonic discourses. Postcolonial critiques at large will frame this analysis of strategies of domination and resistance, but some discussions from the domain of history, sociology and cultural studies may also enter the debate. In this regard there is a great variety of theories and arguments dealing with the contradictions and incongruities in the question of power relations interconnecting domination and resistance. This study is arranged in three pivotal debates. There is firstly an in-depth discussion of underpinning theories that deal with strategies of domination and resistance in the postcolonial domain This is a threefold task carried out by scrutinising (a) the origins of colonial discourse and its binarist tendencies, (b) the pitfalls of anticolonialist resistance based on dualistic opposites, and (c) the hybrid and insubordinate nature of resistance as an efficient alternative to transcend such binaries. Afterwards I seek to investigate how strategies of diasporic resistance and cultural hybridism employed in the poetry of Linton Kwesi Johnson can contribute to moving away from the limitations of dichotomies and also subvert hegemonic power. And finally, I look at crealisation, mockery and insubordination as strategies of resistance in the postapartheid poetry of Lesego Rampolokeng. Besides that, this project is concerned with the increasing importance of academic studies on postcolonial literatures. The present research aims therefore to analyse postcolonial and post-apartheid poems as strategic techniques to decentre dominant Western rhetoric that tries to naturalise inequalities and injustices in the relations between power holders and the powerless in both local and global contexts

The role of Seed Associations on crop production: how to globalize Brazil in the world seed market?

ABRATES (Brazilian Association of Seed Technology) is a scientific non-profit organization, founded in 1970. Its members consist of research scientists, professors, students and other professionals related to the seed sector, and seed producing companies. The major objectives of ABRATES are: support and stimulate scientific work and teaching on seed technology; disseminate results of scientific and technical papers of interest to the seed sector; cooperate with individuals or entities, public or private, on issues related to seed technology; suggest methods and uniform practices, aimed at improving seed technology in the country. These objectives are achieved by implementing various actions. Three Brazilian Seed Seminars and 17 editions of the Brazilian Seed Congress have been offered. In these events, 7,797 papers were delivered. Eleven editions of the Brazilian Symposium on Seed Pathology, five of the Brazilian Symposium of Forest Seeds, and three of the Brazilian Workshop on Seed Quality Control have been offered by ABRATES. The association edits the Brazilian Seed Journal (Revista Brasileira de Sementes), first published in 1979. A total of 1,722 research papers have been published so far. Since 1990, ABRATES has edited the ABRATES Newsletter (Informativo ABRATES), containing more practical technical articles, news and the abstracts of the Brazilian Seed Congress and other scientific events promoted by the association. In 2012, a new electronic publication was implemented: ABRATES in Focus (ABRATES em Foco), which is a monthly newsletter delivering technical news, interviews, and other information by e-mail. All these three publications can be accessed by the association site (www.abrates.org.br). The association is also in the social network, using Facebook and Twitter. ABRATES edits books and handbooks related to the seed area, dealing with subjects such as seed vigor procedures, sampling, analysis, seed processing, seed pathology and forest seeds. Since 2011, it has been involved in offering training courses to the seed sector, dealing with the specialization of Seed Physiology, Seed Sampling, Seed Analysis, and Seed and Seedling Image Analysis. Basically, all this effort is devoted to the seed production sector, aiming the production of high quality seeds and seedlings of several species

Effect of spatial inhomogeneity on the mapping between strongly interacting fermions and weakly interacting spins

A combined analytical and numerical study is performed of the mapping between strongly interacting fermions and weakly interacting spins, in the framework of the Hubbard, t-J and Heisenberg models. While for spatially homogeneous models in the thermodynamic limit the mapping is thoroughly understood, we here focus on aspects that become relevant in spatially inhomogeneous situations, such as the effect of boundaries, impurities, superlattices and interfaces. We consider parameter regimes that are relevant for traditional applications of these models, such as electrons in cuprates and manganites, and for more recent applications to atoms in optical lattices. The rate of the mapping as a function of the interaction strength is determined from the Bethe-Ansatz for infinite systems and from numerical diagonalization for finite systems. We show analytically that if translational symmetry is broken through the presence of impurities, the mapping persists and is, in a certain sense, as local as possible, provided the spin-spin interaction between two sites of the Heisenberg model is calculated from the harmonic mean of the onsite Coulomb interaction on adjacent sites of the Hubbard model. Numerical calculations corroborate these findings also in interfaces and superlattices, where analytical calculations are more complicated.Comment: 7 pages, 6 figure

Direct measurement of finite-time disentanglement induced by a reservoir

We propose a method for directly probing the dynamics of disentanglement of an initial two-qubit entangled state, under the action of a reservoir. We show that it is possible to detect disentanglement, for experimentally realizable examples of decaying systems, through the measurement of a single observable, which is invariant throughout the decay. The systems under consideration may lead to either finite-time or asymptotic disentanglement. A general prescription for measuring this observable, which yields an operational meaning to entanglement measures, is proposed, and exemplified for cavity quantum electrodynamics and trapped ions.Comment: 4 pages, 2 figure

Controlling the dynamics of a coupled atom-cavity system by pure dephasing : basics and potential applications in nanophotonics

The influence of pure dephasing on the dynamics of the coupling between a two-level atom and a cavity mode is systematically addressed. We have derived an effective atom-cavity coupling rate that is shown to be a key parameter in the physics of the problem, allowing to generalize the known expression for the Purcell factor to the case of broad emitters, and to define strategies to optimize the performances of broad emitters-based single photon sources. Moreover, pure dephasing is shown to be able to restore lasing in presence of detuning, a further demonstration that decoherence can be seen as a fundamental resource in solid-state cavity quantum electrodynamics, offering appealing perspectives in the context of advanced nano-photonic devices.Comment: 10 pages, 7 figure

Abrupt Changes in the Dynamics of Quantum Disentanglement

Entanglement evolution in high dimensional bipartite systems under dissipation is studied. Discontinuities for the time derivative of the lower bound of entanglement of formation is found depending on the initial conditions for entangled states. This abrupt changes along the evolution appears as precursors of entanglement sudden death.Comment: 4 pages and 6 figures, submitted for publicatio