Generation and detection of bound entanglement

We propose a method for the experimental generation of two different families of bound entangled states of three qubits. Our method is based on the explicit construction of a quantum network that produces a purification of the desired state. We also suggest a route for the experimental detection of bound entanglement, by employing a witness operator plus a test of the positivity of the partial transposes

Fisher matrix forecasts for astrophysical tests of the stability of the fine-structure constant

We use Fisher Matrix analysis techniques to forecast the cosmological impact of astrophysical tests of the stability of the fine-structure constant to be carried out by the forthcoming ESPRESSO spectrograph at the VLT (due for commissioning in late 2017), as well by the planned high-resolution spectrograph (currently in Phase A) for the European Extremely Large Telescope. Assuming a fiducial model without $\alpha$ variations, we show that ESPRESSO can improve current bounds on the E\"{o}tv\"{o}s parameter---which quantifies Weak Equivalence Principle violations---by up to two orders of magnitude, leading to stronger bounds than those expected from the ongoing tests with the MICROSCOPE satellite, while constraints from the E-ELT should be competitive with those of the proposed STEP satellite. Should an $\alpha$ variation be detected, these measurements will further constrain cosmological parameters, being particularly sensitive to the dynamics of dark energy.Comment: Phys. Lett. B (in press

Fertilização com uréia em superfície em pastagem irrigada e a volatilização de amônia.

A aplicação de uréia em superfície na pastagem pode ocasionar elevadas perdas de amônia por volatilização e uma das alternativas para minimizar esse efeito é a irrigação ou a precipitação logo após a adubação. O objetivo dessa pesquisa foi avaliar o efeito da aplicação de lâminas de água, após a adubação com uréia (75 kgN/ha) na superfície e a lanço em pastagem de colonião, nas perdas de N por volatilização. Foram realizados três experimentos em três épocas, verão, inverno e primavera. O delineamento experimental foi em faixas, em sistema de aspersão em linha, com cinco repetições. Os tratamentos foram quatro níveis de irrigação após a adubação com uréia, sendo três tratamentos com lâminas de água e um controle (sem irrigação). Um dos tratamentos consistia em elevar a umidade do solo à capacidade de campo e os outros dois eram lâminas de água intermediárias aos do controle e capacidade de campo, havendo variação conforme a estação do ano. No verão, a aplicação de apenas 3,2 mm de água elevou a umidade do solo para 52,4% da capacidade de água disponível e reduziu as perdas de N-NH3 para menos de 3,1 % do N aplicado, enquanto a ausência de irrigação provocou perdas de 30,5%. No inverno e na primavera a volatilização de N-NH3 foi baixa, mesmo na ausência de irrigação após a adubação. Na primavera, a irrigação com 16 mm de água elevou a umidade do solo à capacidade de campo e reduziu as perdas para 1,6 % do N aplicado, enquanto no controle as perdas foram de 5%

Is it really possible to grow isotropic on-lattice diffusion-limited aggregates?

In a recent paper (Bogoyavlenskiy V A 2002 \JPA \textbf{35} 2533), an algorithm aiming to generate isotropic clusters of the on-lattice diffusion-limited aggregation (DLA) model was proposed. The procedure consists of aggregation probabilities proportional to the squared number of occupied sites ($k^2$). In the present work, we analyzed this algorithm using the noise reduced version of the DLA model and large scale simulations. In the noiseless limit, instead of isotropic patterns, a $45^\circ$ ($30^\circ$) rotation in the anisotropy directions of the clusters grown on square (triangular) lattices was observed. A generalized algorithm, in which the aggregation probability is proportional to $k^\nu$, was proposed. The exponent $\nu$ has a nonuniversal critical value $\nu_c$, for which the patterns generated in the noiseless limit exhibit the original (axial) anisotropy for $\nu<\nu_c$ and the rotated one (diagonal) for $\nu>\nu_c$. The values $\nu_c = 1.395\pm0.005$ and $\nu_c = 0.82\pm 0.01$ were found for square and triangular lattices, respectively. Moreover, large scale simulations show that there are a nontrivial relation between noise reduction and anisotropy direction. The case $\nu=2$ (\bogo's rule) is an example where the patterns exhibit the axial anisotropy for small and the diagonal one for large noise reduction.Comment: 12 pages, 8 figure

Direct estimation of functionals of density operators by local operations and classical communication

We present a method of direct estimation of important properties of a shared bipartite quantum state, within the "distant laboratories" paradigm, using only local operations and classical communication. We apply this procedure to spectrum estimation of shared states, and locally implementable structural physical approximations to incompletely positive maps. This procedure can also be applied to the estimation of channel capacity and measures of entanglement

Non-destructive studies of prehistoric lithic material culture in the search for sources of geologic raw materials: an overview of techniques and issues

Geological raw materials are an important component of the archaeological record in the Prehistory (namely due to their persistence under buried conditions) and pinpointing their original position on the geological context could give important information about activities of ancient human groups. However, archaeological lithic artefacts impose strict restrictions on analytical procedures due to the need to preserve features with cultural meaning, which might affect the effectiveness of the analytical procedure. We attempt here a critical overview of non-destructive techniques for the search of the source of geological raw materials used to make prehistoric lithic artefacts, highlighting issues involved in the interactions between techniques and study objects. It is emphasized that the success of provenance studies will strongly depend on the sensitivity of the analyses undertaken to the characteristics of the sample, as well as the geological information availableLas materias primas geológicas son un componente importante del registro arqueológico de la Prehistoria (debido a su persistencia en condiciones de enterramiento) y la determinación de su posición original en el contexto geológico podría proporcionar información importante sobre las actividades de los antiguos grupos humanos. Sin embargo, los objetos líticos arqueológicos imponen restricciones estrictas a los procedimientos analíticos debido a la necesidad de preservar elementos con significado cultural, lo que podría afectar a la eficacia del procedimiento analítico. Esta publicación intenta presentar una visión crítica de las técnicas no destructivas para la pesquisa de las fuentes de materias primas geológicas utilizadas en la fabricación de artefactos líticos prehistóricos, resaltando los problemas relacionados con las interacciones entre las técnicas y los objetos de estudio. Se subraya que el éxito de los estudios de procedencia dependerá en gran medida de la sensibilidad de los análisis realizados a las características de la muestra, así como de la información geológica disponible.The Lab2PT - Landscapes, Heritage and Territory laboratory - AUR/04509 is supported by the Portuguese “Fundação para a Ciência e a Tecnologia” (Portuguese funds and where applicable the FEDER co-financing, in the aim of the new partnership agreement PT2020 and COMPETE2020 - POCI 01 0145 FEDER 007528). Pedro Xavier would like to thank the Fundação para a Ciência e a Tecnologia (Foundation for Science and Technology) for PhD scholarship, reference (SFRH/BD/120806/2016) and to the Unidade de Arqueologia da Universidade do Minho (UAUM) for the conditions to perform laboratory work

Aggregation in a mixture of Brownian and ballistic wandering particles

In this paper, we analyze the scaling properties of a model that has as limiting cases the diffusion-limited aggregation (DLA) and the ballistic aggregation (BA) models. This model allows us to control the radial and angular scaling of the patterns, as well as, their gap distributions. The particles added to the cluster can follow either ballistic trajectories, with probability $P_{ba}$, or random ones, with probability $P_{rw}=1-P_{ba}$. The patterns were characterized through several quantities, including those related to the radial and angular scaling. The fractal dimension as a function of $P_{ba}$ continuously increases from $d_f\approx 1.72$ (DLA dimensionality) for $P_{ba}=0$ to $d_f\approx 2$ (BA dimensionality) for $P_{ba}=1$. However, the lacunarity and the active zone width exhibt a distinct behavior: they are convex functions of $P_{ba}$ with a maximum at $P_{ba}\approx1/2$. Through the analysis of the angular correlation function, we found that the difference between the radial and angular exponents decreases continuously with increasing $P_{ba}$ and rapidly vanishes for $P_{ba}>1/2$, in agreement with recent results concerning the asymptotic scaling of DLA clusters.Comment: 7 pages, 6 figures. accepted for publication on PR