Communication Enhancement Through Quantum Coherent Control of NN Channels in an Indefinite Causal-order Scenario

In quantum Shannon theory, transmission of information is enhanced by quantum features. Up to very recently, the trajectories of transmission remained fully classical. Recently, a new paradigm was proposed by playing quantum tricks on two completely depolarizing quantum channels i.e. using coherent control in space or time of the two quantum channels. We extend here this control to the transmission of information through a network of an arbitrary number $N$ of channels with arbitrary individual capacity i.e. information preservation characteristics in the case of indefinite causal order. We propose a formalism to assess information transmission in the most general case of $N$ channels in an indefinite causal order scenario yielding the output of such transmission. Then we explicitly derive the quantum switch output and the associated Holevo limit of the information transmission for $N=2$, $N=3$ as a function of all involved parameters. We find in the case $N=3$ that the transmission of information for three channels is twice of transmission of the two channel case when a full superposition of all possible causal orders is used

Alterações na fertilidade dos solos em áreas de produção familiar de mandioca no Território do Alto Sertão de Alagoas.

O Território do Alto Sertão de Alagoas, também conhecido como Xingó, é formado por oito municípios (Água Branca, Canapi, Delmiro Gouveia, Inhapi, Mata Grande, Olho D?Água do Casado, Pariconha e Piranhas). Esse território possui uma população estimada de 167.660 habitantes (IBGE, 2007), faz divisa com os estados de Sergipe, Bahia e Pernambuco, perfazendo uma área de 3.905,4 km2.bitstream/item/122986/1/Alteracoes-na-fertilidade-COT-89-On-line.pd

The three-body recombination of a condensed Bose gas near a Feshbach resonance

In this paper, we study the three-body recombination rate of a homogeneous dilute Bose gas with a Feshbach resonance at zero temperature. The ground state and excitations of this system are obtained. The three-body recombination in the ground state is due to the break-up of an atom pair in the quantum depletion and the formation of a molecule by an atom from the broken pair and an atom from the condensate. The rate of this process is in good agreement with the experiment on $^{23}$Na in a wide range of magnetic fields.Comment: 10 pages, 2 figures, to be published in Phys. Rev.

A 20 GHz bright sample for {\delta} > +72{\deg}: I. Catalogue

During 2010-2011, the Medicina 32-m dish hosted the 7-feed 18-26.5 GHz receiver built for the Sardinia Radio Telescope, with the goal to perform its commissioning. This opportunity was exploited to carry out a pilot survey at 20 GHz over the area for {\delta} > + 72.3{\deg}. This paper describes all the phases of the observations, as they were performed using new hardware and software facilities. The map-making and source extraction procedures are illustrated. A customised data reduction tool was used during the follow-up phase, which produced a list of 73 confirmed sources down to a flux density of 115 mJy. The resulting catalogue, here presented, is complete above 200 mJy. Source counts are in agreement with those provided by the AT20G survey. This pilot activity paves the way to a larger project, the K-band Northern Wide Survey (KNoWS), whose final aim is to survey the whole Northern Hemisphere down to a flux limit of 50 mJy (5{\sigma}).Comment: 10 pages, 10 figures. Accepted by MNRA

Continuous-variable entanglement of two bright coherent states that never interacted

We study continuous-variable entanglement of bright quantum states in a pair of evanescently coupled nonlinear $\chi^{(2)}$ waveguides operating in the regime of degenerate down-conversion. We consider the case where only the energy of the nonlinearly generated fields is exchanged between the waveguides while the pump fields stay independently guided in each original waveguide. We show that this device, when operated in the depletion regime, entangles the two non-interacting bright pump modes due to a nonlinear cascade effect. It is also shown that two-colour quadripartite entanglement can be produced when certain system parameters are appropriately set. This device works in the traveling-wave configuration, such that the generated quantum light shows a broad spectrum. The proposed device can be easily realized with current technology and therefore stands as a good candidate for a source of bipartite or multipartite entangled states for the emerging field of optical continuous-variable quantum information processing.Comment: 10 pages, 12 figure

Two-dimensional Quantum Black Holes, Branes in BTZ and Holography

We solve semiclassical Einstein equations in two dimensions with a massive source and we find a static, thermodynamically stable, quantum black hole solution in the Hartle-Hawking vacuum state. We then study the black hole geometry generated by a boundary mass sitting on a non-zero tension 1-brane embedded in a three-dimensional BTZ black hole. We show that the two geometries coincide and we extract, using holographic relations, information about the CFT living on the 1-brane. Finally, we show that the quantum black hole has the same temperature of the bulk BTZ, as expected from the holographic principle.Comment: 10 pages, 2 figures, RevTex, ``point particle of mass \mu '' changed with ``massive boundary source'' for better clarity. Action in (50) written in Z_2 symmetric form. Appendix clarified. Minor corrections and references added. Version accepted for pubblication in PRD15 (2006

Manejo de plantas daninhas na cultura da mandioca no Agreste Alagoano.

bitstream/item/145863/1/CT-74.pd

Casimir-like tunneling-induced electronic forces

We study the quantum forces that act between two nearby conductors due to electronic tunneling. We derive an expression for these forces by calculating the flux of momentum arising from the overlap of evanescent electronic fields. Our result is written in terms of the electronic reflection amplitudes of the conductors and it has the same structure as Lifshitz's formula for the electromagnetically mediated Casimir forces. We evaluate the tunneling force between two semiinfinite conductors and between two thin films separated by an insulating gap. We discuss some applications of our results.Comment: 8 pages, 3 figs, submitted to Proc. of QFEXT'05, to be published in J. Phys.