Randomized benchmarking of single and multi-qubit control in liquid-state NMR quantum information processing

Being able to quantify the level of coherent control in a proposed device implementing a quantum information processor (QIP) is an important task for both comparing different devices and assessing a device's prospects with regards to achieving fault-tolerant quantum control. We implement in a liquid-state nuclear magnetic resonance QIP the randomized benchmarking protocol presented by Knill et al (PRA 77: 012307 (2008)). We report an error per randomized $\frac{\pi}{2}$ pulse of $1.3 \pm 0.1 \times 10^{-4}$ with a single qubit QIP and show an experimentally relevant error model where the randomized benchmarking gives a signature fidelity decay which is not possible to interpret as a single error per gate. We explore and experimentally investigate multi-qubit extensions of this protocol and report an average error rate for one and two qubit gates of $4.7 \pm 0.3 \times 10^{-3}$ for a three qubit QIP. We estimate that these error rates are still not decoherence limited and thus can be improved with modifications to the control hardware and software.Comment: 10 pages, 6 figures, submitted versio

The Quantum Mechanics of Hyperion

This paper is motivated by the suggestion [W. Zurek, Physica Scripta, T76, 186 (1998)] that the chaotic tumbling of the satellite Hyperion would become non-classical within 20 years, but for the effects of environmental decoherence. The dynamics of quantum and classical probability distributions are compared for a satellite rotating perpendicular to its orbital plane, driven by the gravitational gradient. The model is studied with and without environmental decoherence. Without decoherence, the maximum quantum-classical (QC) differences in its average angular momentum scale as hbar^{2/3} for chaotic states, and as hbar^2 for non-chaotic states, leading to negligible QC differences for a macroscopic object like Hyperion. The quantum probability distributions do not approach their classical limit smoothly, having an extremely fine oscillatory structure superimposed on the smooth classical background. For a macroscopic object, this oscillatory structure is too fine to be resolved by any realistic measurement. Either a small amount of smoothing (due to the finite resolution of the apparatus) or a very small amount of environmental decoherence is sufficient ensure the classical limit. Under decoherence, the QC differences in the probability distributions scale as (hbar^2/D)^{1/6}, where D is the momentum diffusion parameter. We conclude that decoherence is not essential to explain the classical behavior of macroscopic bodies.Comment: 17 pages, 24 figure

The ConStratO model of handover: a tool to support technology design and evaluation

Handovers are a specific kind of multidisciplinary team meeting. Shift handovers and transfers are both regular features of hospital work but there is currently great variation in how such handovers are conducted, presenting a challenging for those seeking to develop technology to support handover. This paper presents the ConStratO model of handover, which captures aspects of the context that influence how the handover is conducted, a range of different handover strategies relating to different aspects of the handover, and possible outcomes of handover. The model is based on detailed data collection in a range of clinical settings. We present the model as a tool for developing and evaluating technology support for handover

Testing integrability with a single bit of quantum information

We show that deterministic quantum computing with a single bit (DQC1) can determine whether the classical limit of a quantum system is chaotic or integrable using O(N) physical resources, where $N$ is the dimension of the Hilbert space of the system under study. This is a square root improvement over all known classical procedures. Our study relies strictly on the random matrix conjecture. We also present numerical results for the nonlinear kicked top.Comment: Minor changes taking into account Howard Wiseman's comment: quant-ph/0305153. Accepted for publication in Phys. Rev.

Preliminary results for RR Lyrae stars and Classical Cepheids from the Vista Magellanic Cloud (VMC) Survey

The Vista Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting $K_S$-band time series photometry of the system formed by the two Magellanic Clouds (MC) and the "bridge" that connects them. These data are used to build $K_S$-band light curves of the MC RR Lyrae stars and Classical Cepheids and determine absolute distances and the 3D geometry of the whole system using the $K$-band period luminosity ($PLK_S$), the period - luminosity - color ($PLC$) and the Wesenhiet relations applicable to these types of variables. As an example of the survey potential we present results from the VMC observations of two fields centered respectively on the South Ecliptic Pole and the 30 Doradus star forming region of the Large Magellanic Cloud. The VMC $K_S$-band light curves of the RR Lyrae stars in these two regions have very good photometric quality with typical errors for the individual data points in the range of $\sim$ 0.02 to 0.05 mag. The Cepheids have excellent light curves (typical errors of $\sim$ 0.01 mag). The average $K_S$ magnitudes derived for both types of variables were used to derive $PLK_S$ relations that are in general good agreement within the errors with the literature data, and show a smaller scatter than previous studies.Comment: 7 pages, 6 figure. Accepted for publication in Astrophysics and Space Science. Following a presentation at the conference "The Fundamental Cosmic Distance Scale: State of the Art and the Gaia Perspective", Naples, May 201

DA495 - an aging pulsar wind nebula

We present a radio continuum study of the pulsar wind nebula (PWN) DA 495 (G65.7+1.2), including images of total intensity and linear polarization from 408 to 10550 MHz based on the Canadian Galactic Plane Survey and observations with the Effelsberg 100-m Radio Telescope. Removal of flux density contributions from a superimposed \ion{H}{2} region and from compact extragalactic sources reveals a break in the spectrum of DA 495 at 1.3 GHz, with a spectral index ${\alpha}={-0.45 \pm 0.20}$ below the break and ${\alpha}={-0.87 \pm 0.10}$ above it (${S}_\nu \propto{\nu^{\alpha}}$). The spectral break is more than three times lower in frequency than the lowest break detected in any other PWN. The break in the spectrum is likely the result of synchrotron cooling, and DA 495, at an age of $\sim$20,000 yr, may have evolved from an object similar to the Vela X nebula, with a similarly energetic pulsar. We find a magnetic field of $\sim$1.3 mG inside the nebula. After correcting for the resulting high internal rotation measure, the magnetic field structure is quite simple, resembling the inner part of a dipole field projected onto the plane of the sky, although a toroidal component is likely also present. The dipole field axis, which should be parallel to the spin axis of the putative pulsar, lies at an angle of {\sim}50\degr east of the North Celestial Pole and is pointing away from us towards the south-west. The upper limit for the radio surface brightness of any shell-type supernova remnant emission around DA 495 is $\Sigma_{1 GHz} \sim 5.4 \times 10^{-23}$ OAWatt m$^{-2}$ Hz$^{-1}$ sr$^{-1}$ (assuming a radio spectral index of $\alpha = -0.5$), lower than the faintest shell-type remnant known to date.Comment: 25 pages, accepted by Ap

INFLUÊNCIA DA PRECIPITAÇÃO NOS MANGUEZAIS DA BARRA DO RIBEIRA – IGUAPE/SP

The mangrove, coastal ecosystem defined as a transition between terrestrialand marine environment is characterized as a salinized environment with aconstant flooding caused by tides. Emphasizing the System area CoastalCananéia - Iguape, its importance is related to the biomass production, insertedinto the natural bioenergetics system, increasing the productivity of the coastalzone with the introduction of organic particles. This means vegetal communitiesare adapted to many physical conditionants the active in the coastal zones,including the climate conditionants. This article is part of a larger work, whichpurpose is contributes to the comprehension of variability of the climaticattributes and their influence on the mangrove vegetation. Here are presentedthe data and analysis of the precipitation and interception of rain by the canopyof the mangrove forest located in Barra do Ribeira-Iguape/SP. A microclimatictower was installed with two meteorological stations and each one had raingauge to obtain an analysis of the variation of precipitation above and below thecanopy of mangrove. More sixteen rain gauges were installed in an area of 400m². Our research results shows that in microclimatic scales the main control forthe variation of climatic attributes is the canopy, mainly in rainfall distributionbelow the canopy, which consequently influences in the distribution ofvegetables species in the environment. It was found also that the amount ofrainfall that effectively reaches the ground and how this is redistributed withinthe environment depends on the density of the canopy and its twigs and trunks.To the mangrove this process is important because the amount of rain thateffectively reaches the soil helps to reduce salinity in the environment and isdeterminant for the type of predominant species in the mangrove. This projectcounted on the financing of the CNPq, process referring number 470434/2006-6to the proclamation MCT/CNPq 02/2006 - Universal.O manguezal, definido como um ecossistema costeiro de transição entre osambientes terrestres e marinhos caracteriza-se por ambiente salinizado e pelaconstante inundação causada por marés. Com destaque na área do SistemaCosteiro Cananéia – Iguape, sua importância maior está relacionada à produçãode biomassa, inserida no sistema bioenergético natural, aumentando aprodutividade da zona costeira com a introdução de particulados orgânicos.Representam comunidades vegetais adaptadas a várias condicionantes físicasatuantes nas zonas costeiras, entre elas, as climáticas. O presente artigo fazparte de um trabalho maior, que tem como objetivo contribuir com oentendimento da variação dos atributos climáticos e sua influência na vegetaçãodo manguezal. No entanto, aqui serão apresentados os dados e as análises doatributo precipitação, bem como a interceptação da precipitação pelo dossel domanguezal, localizado na Barra do Ribeira-Iguape/SP. Para isso, foi instaladauma torre microclimática contendo duas estações meteorológicas, com umpluviômetro cada, de forma a obter uma análise da variação da precipitaçãoacima e abaixo do dossel de manguezal. Além de 16 pluviômetros totalizadoresao longo de uma área de 400 m². Verificou-se que, na escala de trabalhomicroclimática, o dossel é o principal controle para a variação dos atributosclimáticos, principalmente na distribuição pluviométrica abaixo desse dossel, oque, consequentemente, influencia na distribuição das espécies vegetais doambiente. Constatou-se que a quantidade de precipitação que efetivamenteatinge o solo e a forma com que ela é redistribuída dentro do ambiente dependeda densidade do dossel e de suas ramificações de galhos e caule. Para omanguezal esse processo é importante, visto que a quantidade de chuva queefetivamente atinge o solo contribuir para a diminuição da salinidade presenteno ambiente, sendo determinante para o tipo de espécie predominante no manguezal. Esse projeto foi financiamento pelo CNPq, processo número470434/2006-6 referente ao edital MCT/CNPq 02/2006 – Universal

Doping dependence of phonon and quasiparticle heat transport of pure and Dy-doped Bi_2Sr_2CaCu_2O_{8+\delta} single crystals

The temperature and magnetic-field (H) dependences of thermal conductivity (\kappa) of Bi_2Sr_2CaCu_2O_{8+\delta} (Bi2212) are systematically measured for a broad doping range by using both pure Bi2212 single crystals with tuned oxygen contents and Bi_2Sr_2Ca_{1-x}Dy_xCu_2O_{8+\delta} (Dy-Bi2212) single crystals with different Dy contents x. In the underdoped samples, the quasiparticle (QP) peak below T_c is strongly suppressed, indicating strong QP scattering by impurities or oxygen defects, whereas the phonon conductivity is enhanced in moderately Dy-doped samples and a phonon peak at 10 K is observed for the first time in Bi2212 system, which means Dy^{3+} ions not only introduce the impurities or point defects but also stabilize the crystal lattice. The subkelvin data show that the QP heat conductivity gradually decreases upon lowering the hole doping level. The magnetic-field dependence of \kappa at temperature above 5 K is mainly due to the QP scattering off vortices. While the underdoped pure Bi2212 show very weak field dependence of \kappa, the Dy-doped samples present an additional "dip"-like term of \kappa(H) at low field, which is discussed to be related to the phonon scattering by free spins of Dy^{3+} ions. For non-superconducting Dy-Bi2212 samples with x \simeq 0.50, an interesting "plateau" feature shows up in the low-T \kappa(H) isotherms with characteristic field at 1 -- 2 T, for which we discuss the possible revlevance of magnon excitations.Comment: 11 pages, 11 figures, accepted for publication in Phys. Rev.