Detection of Spiral photons in Quantum Optics

We show that a new type of photon detector, sensitive to the gradients of electromagnetic fields, should be a useful tool to characterize the quantum properties of spatially-dependent optical fields. As a simple detector of such a kind, we propose using magnetic dipole or electric quadrupole transitions in atoms or molecules and apply it to the detection of spiral photons in Laguerre-Gauss (LG) beams. We show that LG beams are not true hollow beams, due to the presence of magnetic fields and gradients of electric fields on beam axis. This approach paves the way to an analysis at the quantum level of the spatial structure and angular momentum properties of singular light beams.Comment: 5 pages, 4 figure

Time Delays in the Synchronization of Chaotic Coupled Systems with Feedback

The synchronized excitable behavior of two coupled chaotic diode lasers with feedback was experimental and numerically studied. We determine the relation between the observed delay times in synchronized Low Frequency Fluctuation spikes and the coupling and the feedback times in the lasers.Comment: 5 pages, 6 figure

Logarithmic periodicities in the bifurcations of type-I intermittent chaos

The critical relations for statistical properties on saddle-node bifurcations are shown to display undulating fine structure, in addition to their known smooth dependence on the control parameter. A piecewise linear map with the type-I intermittency is studied and a log-periodic dependence is numerically obtained for the average time between laminar events, the Lyapunov exponent and attractor moments. The origin of the oscillations is built in the natural probabilistic measure of the map and can be traced back to the existence of logarithmically distributed discrete values of the control parameter giving Markov partition. Reinjection and noise effect dependences are discussed and indications are given on how the oscillations are potentially applicable to complement predictions made with the usual critical exponents, taken from data in critical phenomena.Comment: 4 pages, 6 figures, accepted for publication in PRL (2004

Transferring orbital and spin angular momenta of light to atoms

Light beams carrying orbital angular momentum, such as Laguerre-Gaussian beams, give rise to the violation of the standard dipolar selection rules during the interaction with matter yielding, in general, an exchange of angular momentum larger than hbar per absorbed photon. By means of ab initio 3D numerical simulations, we investigate in detail the interaction of a hydrogen atom with intense Gaussian and Laguerre-Gaussian light pulses. We analyze the dependence of the angular momentum exchange with the polarization, the orbital angular momentum, and the carrier-envelope phase of light, as well as with the relative position between the atom and the light vortex. In addition, a quantum-trajectory approach based on the de Broglie-Bohm formulation of quantum mechanics is used to gain physical insight into the absorption of angular momentum by the hydrogen atom

Octopus insularis (Cephalopoda: Octopodidae) on the tropical coast of Brazil: where it lives and what it eats

Abstract Octopus insularis is the dominant octopus in the shallow tropical waters of the coast and oceanic islands in the North and Northeast of Brazil. Is the abundance, distribution, habitat and diet of this species on the continent the same as in oceanic islands? These factors were evaluated in seeking these answers at two areas of occurrence of Octopus insularis on the coast of Rio Grande do Norte, Brazil. Three main types of habitats were described where the species is concentrated, being: Deep Reefs (Reefs of Risca) (> 15 m), Flat Biogenic Plateaus (Restingas) (5-15 m) and Shallow Sedimentary Reefs (Pirangi reefs) (< 5 m). An aggregate spatial distribution was verified, along with bathymetric segregation in which small individuals occupied shallow areas. Regarding diet, O. insularis consumed mainly crustaceans (68%) in shallow reef areas, bivalves (86%) in biogenic plateau areas, and gastropods (33%) in deep reef areas. The characterization of new occurring habitats, such as the area of biogenic plateau, and changes in their diet due to habitat function have shown that O. insularis occupies a broader niche than has been described in literature to date, expanding our knowledge on the ecology and biology of this octopus species of economic interest