Robustness of bipartite Gaussian entangled beams propagating in lossy channels

Subtle quantum properties offer exciting new prospects in optical communications. Quantum entanglement enables the secure exchange of cryptographic keys and the distribution of quantum information by teleportation. Entangled bright beams of light attract increasing interest for such tasks, since they enable the employment of well-established classical communications techniques. However, quantum resources are fragile and undergo decoherence by interaction with the environment. The unavoidable losses in the communication channel can lead to a complete destruction of useful quantum properties -- the so-called "entanglement sudden death". We investigate the precise conditions under which this phenomenon takes place for the simplest case of two light beams and demonstrate how to produce states which are robust against losses. Our study sheds new light on the intriguing properties of quantum entanglement and how they may be tamed for future applications.Comment: To be published - Nature Photonic

Disentanglement in Bipartite Continuous-Variable Systems

Entanglement in bipartite continuous-variable systems is investigated in the presence of partial losses, such as those introduced by a realistic quantum communication channel, e.g. by propagation in an optical fiber. We find that entanglement can vanish completely for partial losses, in a situa- tion reminiscent of so-called entanglement sudden death. Even states with extreme squeezing may become separable after propagation in lossy channels. Having in mind the potential applications of such entangled light beams to optical communications, we investigate the conditions under which entanglement can survive for all partial losses. Different loss scenarios are examined and we derive criteria to test the robustness of entangled states. These criteria are necessary and sufficient for Gaussian states. Our study provides a framework to investigate the robustness of continuous-variable entanglement in more complex multipartite systems.Comment: Phys. Rev. A (in press

Modeling the ecology and evolution of biodiversity: Biogeographical cradles, museums, and graves

Individual processes shaping geographical patterns of biodiversity are increasingly understood, but their complex interactions on broad spatial and temporal scales remain beyond the reach of analytical models and traditional experiments. To meet this challenge, we built a spatially explicit, mechanistic simulation model implementing adaptation, range shifts, fragmentation, speciation, dispersal, competition, and extinction, driven by modeled climates of the past 800,000 years in South America. Experimental topographic smoothing confirmed the impact of climate heterogeneity on diversification. The simulations identified regions and episodes of speciation (cradles), persistence (museums), and extinction (graves). Although the simulations had no target pattern and were not parameterized with empirical data, emerging richness maps closely resembled contemporary maps for major taxa, confirming powerful roles for evolution and diversification driven by topography and climate

Programa de educação parental "(Re)Construir Famílias" : um projeto de investigação-ação

Este projeto de investigação-ação tem como objetivo a proposta do programa de educação parental “(Re)Construir Famílias” e do plano de investigação necessário para avaliar a sua eficácia na promoção de uma melhoria no exercício da parentalidade em pais sinalizados/acompanhados no âmbito das situações de risco para a criança/jovem. A partir do diagnóstico realizado, procurou-se apresentar um programa que acrescenta a dimensão do bem-estar dos pais, aos aspetos geralmente trabalhados na intervenção parental deste tipo. Sugere-se um programa assente na parentalidade positiva que possa ser implementado por um Educador Social (em equipa) atendendo às dimensões de educação para a saúde e apoio à gestão da vida diária incluídas na planificação da intervenção. O plano de investigação concretiza-se numa metodologia de teste-reteste com grupo experimental e de controlo, ambos constituídos por 12 pais. Será aplicado um conjunto de instrumentos (Questionário de Caracterização Geral construído neste trabalho, Escala de Satisfação com a Vida, Escala de Afetividade Positiva e Afetividade Negativa e Questionário das Práticas Parentais) que permitirá avaliar a eficácia da proposta de intervenção. Os dados serão analisados recorrendo ao Statistical Package for Social Sciences (SPSS versão IBM 21), assumindo o grau de confiança de 95%. Espera-se que este programa promova ajustes na parentalidade destes pais e que, em última instância, permita acrescentar contributos que promovam a proteção das crianças e jovens em risco (re)construindo as suas famílias.This action research project aims to propose the parental education program “(Re)Constructing Families" and the research plan needed to assess its effectiveness promoting improvement in parenthood in families under risk situations for the child/youth. Based on the diagnostic conducted, we planned a program that adds the dimension of well-being of parents to the usually worked aspects in parental intervention. It is suggested a program based on positive parenthood that can be implemented by a Social Educator (working in a team) due to the dimensions of health education and support to the management of daily life, included in the intervention presented. The research plan adopts test-retest method with experimental and control groups, both consisting of 12 parents. We will apply a set of instruments (General Characterization Questionnaire constructed in this project, Satisfaction with Life Scale, Positive Affect and Negative Affect Schedule and Parenting Practices Questionnaire) that will evaluate the effectiveness of the proposed intervention. Data will be analyzed using the Statistical Package for Social Sciences (SPSS version 21 IBM), assuming the 95% level of confidence. It is hoped that this program promotes adjustments in parenthood and ultimately add contributions to the protection of children and youth at risk (re)constructing their families

Entanglement of two-mode Gaussian states: characterization and experimental production and manipulation

A powerful theoretical structure has emerged in recent years on the characterization and quantification of entanglement in continuous-variable systems. After reviewing this framework, we will illustrate it with an original set-up based on a type-II OPO with adjustable mode coupling. Experimental results allow a direct verification of many theoretical predictions and provide a sharp insight into the general properties of two-mode Gaussian states and entanglement resource manipulation

Quantum coherent control of highly multipartite continuous-variable entangled states by tailoring parametric interactions

The generation of continuous-variable multipartite entangled states is important for several protocols of quantum information processing and communication, such as one-way quantum computation or controlled dense coding. In this article we theoretically show that multimode optical parametric oscillators can produce a great variety of such states by an appropriate control of the parametric interaction, what we accomplish by tailoring either the spatio-temporal shape of the pump, or the geometry of the nonlinear medium. Specific examples involving currently available optical parametric oscillators are given, hence showing that our ideas are within reach of present technology.Comment: 14 pages, 5 figure