Modulational instability of spatially broadband nonlinear optical pulses in four-state atomic systems

The modulational instability of broadband optical pulses in a four-state atomic system is investigated. In particular, starting from a recently derived generalized nonlinear Schr\"odinger equation, a wave-kinetic equation is derived. A comparison between coherent and random phase wave states is made. It is found that the spatial spectral broadening can contribute to the nonlinear stability of ultra-short optical pulses. In practical terms, this could be achieved by using random phase plate techniques.Comment: 9 pages, 3 figures, to appear in Phys. Rev.

Classical Rotons in Cold Atomic Traps

We predict the emergence of a roton minimum in the dispersion relation of elementary excitations in cold atomic gases in the presence of diffusive light. In large magneto-topical traps, multiple-scattering of light is responsible for the collective behavior of the system, which is associated to an effective Coulomb-like interaction between the atoms. In optically thick clouds, the re-scattered light undergoes diffusive propagation, which is responsible for a stochastic short-range force acting on the atoms. We show that the dynamical competition between these two forces results on a new polariton mode, which exhibits a roton minimum. Making use of Feynman's formula for the static structure factor, we show that the roton minimum is related to the appearance of long-range order in the system.Comment: 5 pages, 3 figure

Entanglement versus Quantum Discord in Two Coupled Double Quantum Dots

We study the dynamics of quantum correlations of two coupled double quantum dots containing two excess electrons. The dissipation is included through the contact with an oscillator bath. We solve the Redfield master equation in order to determine the dynamics of the quantum discord and the entanglement of formation. Based on our results, we find that the quantum discord is more resistant to dissipation than the entanglement of formation for such a system. We observe that this characteristic is related to whether the oscillator bath is common to both qubits or not and to the form of the interaction Hamiltonian. Moreover, our results show that the quantum discord might be finite even for higher temperatures in the asymptotic limit.Comment: 14 pages, 8 figures (new version is the final version to appear in NJP

Amplification and generation of ultra-intense twisted laser pulses via stimulated Raman scattering

Twisted Laguerre-Gaussian lasers, with orbital angular momentum and characterised by doughnut shaped intensity profiles, provide a transformative set of tools and research directions in a growing range of fields and applications, from super-resolution microcopy and ultra-fast optical communications to quantum computing and astrophysics. The impact of twisted light is widening as recent numerical calculations provided solutions to long-standing challenges in plasma-based acceleration by allowing for high gradient positron acceleration. The production of ultrahigh intensity twisted laser pulses could then also have a broad influence on relativistic laser-matter interactions. Here we show theoretically and with ab-initio three-dimensional particle-in-cell simulations, that stimulated Raman backscattering can generate and amplify twisted lasers to Petawatt intensities in plasmas. This work may open new research directions in non-linear optics and high energy density science, compact plasma based accelerators and light sources.Comment: 18 pages, 4 figures, 1 tabl

Neutrino magnetohydrodynamics

A new neutrino magnetohydrodynamics (NMHD) model is formulated, where the effects of the charged weak current on the electron-ion magnetohydrodynamic fluid are taken into account. The model incorporates in a systematic way the role of the Fermi neutrino weak force in magnetized plasmas. A fast neutrino-driven short wavelengths instability associated with the magnetosonic wave is derived. Such an instability should play a central role in strongly magnetized plasma as occurs in supernovae, where dense neutrino beams also exist. In addition, in the case of nonlinear or high frequency waves, the neutrino coupling is shown to be responsible for breaking the frozen-in magnetic field lines condition even in infinite conductivity plasmas. Simplified and ideal NMHD assumptions were adopted and analyzed in detail

Correlação entre distância genética e heterose para comprimento de panícula por cruzamento dialélico entre acessos de arroz (Oryza sativa L.) de base genética ampla.

O objetivo desse trabalho foi correlacionar os dados de distância genética de Rogers modificada por Wright e a heterose observada no caractere comprimento de panícula, um dos componentes de produtividade do arroz, dos 120 híbridos obtidos nesses cruzamentos

Avaliação do capim-marandu sob déficit hídrico em casa de vegetação, no período de estabelecimento.

O objetivo deste trabalho foi avaliar o perfilhamento e a produção de biomassa do capim-marandu no período de estabelecimento, sob influência do déficit hídrico. Realizou-se o experimento em casa-de-vegetação na Embrapa Pecuária Sudeste, sob delineamento em blocos completos casualizados com arranjo fatorial 3x3+1. Os tratamentos referiram-se à suspensão da irrigação em diferentes épocas do estabelecimento (semeadura, germinação e perfilhamento primário) até que o solo apresentasse teor de água equivalente a 75, 50 e 25% da capacidade de armazenamento de água disponível no solo (CAD), além da testemunha que não sofreu restrição hídrica. As avaliações de número de perfilhos surgidos por vaso foram realizadas semanalmente, por cinco semanas, a partir do início do perfilhamento. Uma coleta de biomassa foi realizada aproximadamente 30 dias após o término do último tratamento, período em que o solo foi mantido próximo a capacidade de campo. O perfilhamento e a produção de biomassa do capim-marandu são reduzidos quando o déficit hídrico é suficiente para que o teor de água no solo atinja 25%CAD, durante a fase de estabelecimento, independente da época em que ocorra a escassez hídrica