Using continuous measurement to protect a universal set of quantum gates within a perturbed decoherence-free subspace

We consider a universal set of quantum gates encoded within a perturbed decoherence-free subspace of four physical qubits. Using second-order perturbation theory and a measuring device modeled by an infinite set of harmonic oscillators, simply coupled to the system, we show that continuous observation of the coupling agent induces inhibition of the decoherence due to spurious perturbations. We thus advance the idea of protecting or even creating a decoherence-free subspace for processing quantum information.Comment: 7 pages, 1 figure. To be published in Journal of Physics A: Mathematical and Genera

Quantum Control of a Single Qubit

Measurements in quantum mechanics cannot perfectly distinguish all states and necessarily disturb the measured system. We present and analyse a proposal to demonstrate fundamental limits on quantum control of a single qubit arising from these properties of quantum measurements. We consider a qubit prepared in one of two non-orthogonal states and subsequently subjected to dephasing noise. The task is to use measurement and feedback control to attempt to correct the state of the qubit. We demonstrate that projective measurements are not optimal for this task, and that there exists a non-projective measurement with an optimum measurement strength which achieves the best trade-off between gaining information about the system and disturbing it through measurement back-action. We study the performance of a quantum control scheme that makes use of this weak measurement followed by feedback control, and demonstrate that it realises the optimal recovery from noise for this system. We contrast this approach with various classically inspired control schemes.Comment: 12 pages, 7 figures, v2 includes new references and minor change

Alternative fidelity measure for quantum states

We propose an alternative fidelity measure (namely, a measure of the degree of similarity) between quantum states and benchmark it against a number of properties of the standard Uhlmann-Jozsa fidelity. This measure is a simple function of the linear entropy and the Hilbert-Schmidt inner product between the given states and is thus, in comparison, not as computationally demanding. It also features several remarkable properties such as being jointly concave and satisfying all of "Jozsa's axioms". The trade-off, however, is that it is supermultiplicative and does not behave monotonically under quantum operations. In addition, new metrics for the space of density matrices are identified and the joint concavity of the Uhlmann-Jozsa fidelity for qubit states is established.Comment: 12 pages, 3 figures. v2 includes minor changes, new references and new numerical results (Sec. IV

The Azorean Biodiversity Portal: an internet database for regional biodiversity outreach

Copyright © 2010 The Natural History Museum.There is a growing interest in academia to provide biodiversity data to both the scientific community and the public. We present an internet database of the terrestrial lichens, bryophytes, vascular plants, molluscs, arthropods, vertebrates and coastal invertebrates of the Azores archipelago (Portugal, North Atlantic): the Azorean Biodiversity Portal (ABP, http://www.azoresbioportal.angra.uac.pt/). This is a unique resource for fundamental research in systematics, biodiversity, education and conservation management. The ABP was based on a regional species database (ATLANTIS), comprised of grid-based spatial incidence information for c. 5000 species. Most of the data rely on a comprehensive literature survey (dating back to the 19th century) as well as unpublished records from recent field surveys in the Azores. The ABP disseminates the ATLANTIS database to the public, allowing universal, unrestricted access to much of its data. Complementarily, the ABP includes additional information of interest to the general public (e.g. literature on Macaronesian biodiversity) together with images from collections and/or live specimens for many species. In this contribution we explain the implementation of a regional biodiversity database, its architecture, achievements and outcomes, strengths and limitations; we further include a number of suggestions in order to implement similar initiatives

Determinação das curvas de secagem das sementes de andiroba em secador solar

The oil of crabwood is commonly extracted in Amazon by traditional or by pressing method. The extraction efficiency is related to the heating and water content of the seeds. Thus, the determination of a drying model that represent satisfactorily the experimental data is of paramount importance to minimize the changes introduced by the process, consequently obtaining a quality product. The objective of this study was to describe the drying kinetics of seeds of crabwood as well as adjust the mathematical models to the experimental data, using solar dryer. The coefficient of determination, the magnitude of the mean relative error and standard deviation of the estimate was used as the criterion of fit of mathematical models. Drying in a shorter period of time (14 days) of Carapa surinamensis to reach the water equilibrium content (12.28%) may be attributed to the smaller size of the seeds and the greater amount of oil compared to Carapa guianensis. Logarithmic and Midilli et al. were the model that best fitted the experimental data for seeds of both species of Andiroba. © 2015, Departamento de Engenharia Agricola - UFCG/Cnpq. All rights reserved

Computer-assisted tomography for studies of an Albaqualf

Na busca de técnicas mais apuradas para a determinação e avaliação de parâmetros físicos do solo com aplicabilidade em várzeas, vem se destacando a tomografia computadorizada, por medir a densidade e a umidade com boa sensibilidade e alta resolução espacial. O presente trabalho teve como objetivo descrever aspectos e procedimentos da calibração de um minitomógrafo de raios-X e gama para estudo da densidade e umidade de um Planossolo no Rio Grande do Sul, bem como estabelecer parâmetros estatísticos para sua adequada utilização. A calibração do minitomógrafo foi obtida pela regressão linear entre as unidades tomográficas (UT), apresentadas pelo programa de reconstrução de imagem, e os coeficientes de atenuação linear (µl, cm-1), medidos por transmissão direta de raios gama, em amostras dos horizontes A e B do Planossolo, água destilada, benzina e alumínio. Para as medidas de transmissão direta de radiação utilizaram-se recipientes com água destilada, benzina, solo e Al, obtendo-se as seguintes fórmulas para o cálculo da densidade do solo no horizonte A: Ds = [(UT/986,16)-(0,200xq)]/0,267; e no horizonte B: Ds = [(UT/986,16)-(0,200xq)]/0,297, em que UT é o valor médio de UT em cada linha e q é a umidade volumétrica da amostra de solo, em m3 m-3. Com as configurações obtidas, verificou-se variabilidade média de 2,74% e 0,73%, respectivamente, em termos de homogeneidade e repetibilidade. Os erros atribuídos ao equipamento são de 0,051 e 0,046 Mg m-3, respectivamente, nos horizontes A e B, revelando precisão e adaptabilidade no emprego da técnica em estudos do Planossolo._________________________________________________________________________________ ABSTRACT: In order to find better techniques to evaluate the soil physical parameters applied to lowland soils, the computerized tomography has been used to measure soil density and water content with accuracy and high spatial resolution. This work was carried out in order to describe features and calibration procedures of a computerized minitomographer using X-ray and gama-rays as sources of radiation and to establish suitable statistical parameters on the study of soil bulk density and water content in a Planosol (Albaqualf) from Rio Grande do Sul State, Brazil. The minitomographer calibration was obtained from the linear regression equation among the tomography's unities (TU) presented by the image reconstruction program and the linear attenuation coefficient (µl, cm-1), by the measurement of direct transmission of g-rays as source of radiation in soil samples from A and B horizons, distilled water, benzin and aluminum. In order to get measures of the direct radiation transmission, containers with distilled water, benzin, soil and aluminum were used to obtain the following equations to calculate soil bulk density in the A horizon: Ds = [(TU/986.16)-(0.200xq)]/0.267 and in the B horizon: Ds = [(TU/986.16)-(0.200xq)]/0.297, where TU is the mean value in the line and q is the soil volumetric water content (m3 m-3). The obtained configurations allowed to attain average variabilities of 2.74% and 0.73% for homogeneity and repeatability, respectively. The expected errors related to the equipment are 0.051 and 0.046 Mg m-3, to the A and B horizons, respectively. The results showed the technique accuracy and adaptability in the studies of the physical characteristics of a Planosol

Diving into the vertical dimension of elasmobranch movement ecology

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements