Magnetic control of the pair creation in spatially localized supercritical fields

We examine the impact of a perpendicular magnetic field on the creation mechanism of electron-positron pairs in a supercritical static electric field, where both fields are localized along the direction of the electric field. In the case where the spatial extent of the magnetic field exceeds that of the electric field, quantum field theoretical simulations based on the Dirac equation predict a suppression of pair creation even if the electric field is supercritical. Furthermore, an arbitrarily small magnetic field outside the interaction zone can bring the creation process even to a complete halt, if it is sufficiently extended. The mechanism for this magnetically induced complete shutoff can be associated with a reopening of the mass gap and the emergence of electrically dressed Landau levels

Entanglement and interference between different degrees of freedom of photons states

In this paper, photonic entanglement and interference are described and analyzed with the language of quantum information process. Correspondingly, a photon state involving several degrees of freedom is represented in a new expression based on the permutation symmetry of bosons. In this expression, each degree of freedom of a single photon is regarded as a qubit and operations on photons as qubit gates. The two-photon Hong-Ou-Mandel interference is well interpreted with it. Moreover, the analysis reveals the entanglement between different degrees of freedom in a four-photon state from parametric down conversion, even if there is no entanglement between them in the two-photon state. The entanglement will decrease the state purity and photon interference visibility in the experiments on a four-photon polarization state.Comment: 11 pages and 2 figure

The Iberian Massif of western Asturias and Lugo: a record of landscape forming processes during 107 time-scales.

El relieve transitorio del occidente Asturiano y Lugo, desarrollado sobre rocas del Macizo Ibérico, contiene información sobre los procesos pasados y recientes que condicionan la topográfica. Un análisis geomorfológico, basado en el uso de Sistemas de Información Geográfica, combinado con técnicas de termocronología de baja temperatura y de análisis de isótopos cosmogénicos, ha permitido identificar varios componentes del paisaje con edades y significados geodinámicos diferentes. Estos son: 1) paleosuperficies de bajo relieve con bajas tasas de denudación, interpretadas como relictos de un periodo entre los 100 y 45 Ma en que se desarrollaron relieves maduros; 2) pequeños ríos costeros que presentan tasas de denudación moderadas asociadas a una lenta elevación del terreno durante el Neógeno; 3) una ancha superficie de abrasión submarina, elevada lentamente (0.07-0.15 mm/a) sobre el nivel del mar desde hace 1.5 Ma. Las rocas de esta región registran tasas de exhumación más altas antes del Cretácico Superior, durante la extensión Mesozoica en el Atlántico y Golfo de Vizcaya. Las tasas de exhumación se redujeron durante el periodo de relativa estabilidad tectónica iniciado después de la ruptura continental en el Cretácico Inferior. El sistema de denudación ha permanecido poco eficiente durante la elevación topográfica iniciada en el Eoceno.Estos estudios han sido financiados a través de los proyectos BTE2002-00330, CGL2005-24204 y CGL2007-60230/BTE de los Ministerios de Educación y Ciencia y de Ciencia e Innovación. Se incluyen en el marco del proyecto “TOPO-Iberia”, Consolider-Ingenio 2010, CSD2006-00041.Peer Reviewe

Double Ionization by Strong Elliptically Polarized Laser Pulses

We join the tribute to Professor N.B. Delone in this memorial issue by presenting the results of new calculations on the effects of ellipticity on double ionization by short and strong near-optical laser pulses.Comment: 3 pages, 4 figures, accepted in Professor N.B. Delone's memorial issu

Multipartite entanglement characterization of a quantum phase transition

A probability density characterization of multipartite entanglement is tested on the one-dimensional quantum Ising model in a transverse field. The average and second moment of the probability distribution are numerically shown to be good indicators of the quantum phase transition. We comment on multipartite entanglement generation at a quantum phase transition.Comment: 10 pages, 6 figures, final versio

A mapping approach to synchronization in the "Zajfman trap": stability conditions and the synchronization mechanism

We present a two particle model to explain the mechanism that stabilizes a bunch of positively charged ions in an "ion trap resonator" [Pedersen etal, Phys. Rev. Lett. 87 (2001) 055001]. The model decomposes the motion of the two ions into two mappings for the free motion in different parts of the trap and one for a compressing momentum kick. The ions' interaction is modelled by a time delay, which then changes the balance between adjacent momentum kicks. Through these mappings we identify the microscopic process that is responsible for synchronization and give the conditions for that regime.Comment: 12 pages, 9 figures; submitted to Phys Rev

Correlation effects in two-electron model atoms in intense laser fields, Phys

We report an efficient implementation of a spatial two-zone method for solving Schrödinger's equation numerically, using a canonical basis set decomposition, and also its application to two-electron wave functions in a study of double multiphoton ionization. We make the first calculation of the time-dependent degree of electron correlation for this poorly understood process. Our results show a particularly sensitive window of intensities coinciding exactly with the well-known "knee" regime in ion-count data. PACS numbers: 32.80. Rm, 32.80.Fb, 42.50.Hz To date, almost all of the theoretical understanding of multiphoton processes of atoms in intense laser fields has been based on the single active electron picture. Even two-electron ionization can be so interpreted if the electrons are ejected sequentially via the AmmosovDelone-Krainov (ADK) mechanism We believe that it will prove valuable to have a better command of the role of electron-electron interaction and correlation in the two-electron ionization process than is presently available. Fundamentally, one knows that all nontrivial effects of correlation are connected to the nonfactorable e-e coupling term in the two-electron Hamiltonian, but little more than this is known. It is not known, for example, whether this term plays a persistent role during the ionization process, or if there is an intensity threshold where its effect "turns on" or "turns off," or even if there is a particularly sensitive window of intensities where the effect of correlation is most active. It is also not known how the effect of electron correlation is synchronized, if at all, with the time development of the ionizing field. Electron correlation, per se, has not been isolated for study. However, as Grobe et al. have shown [13], there are several more or less equally sensible and closely compatible definitions of the degree of electron correlation that are, in principle, open to calculation. The difficulty in taking this route has been obtaining wave functions that are accurate enough over a sufficiently large spatial domain to permit the calculations to be made. In this Letter we show that an expansion of the twoelectron wave function into a sum of Slater determinants of one-electron orthonormal orbitals, as explained below, solves both of these problems. It provides a way to obtain two-electron wave functions efficiently over a much larger spatial domain than has been customary, and it provides the time-dependent degree of correlation during the ionization process. The penalty for this advance is that it can be implemented at the present time only within a one-dimensional (1D) model of a two-electron atom. The 1D model We will begin by confirming that our new implementation of this model is consistent with the most important characteristics of two-electron ionization data. Then we will report the first quantitative results on the timedependent behavior of the degree of two-electron correlation, and relate them to experimentally observed features. 520 0031-9007͞99͞83(3)͞520(4)$15.0

On the absence of bound-state stabilization through short ultra-intense fields

We address the question of whether atomic bound states begin to stabilize in the short ultra-intense field limit. We provide a general theory of ionization probability and investigate its gauge invariance. For a wide range of potentials we find an upper and lower bound by non-perturbative methods, which clearly exclude the possibility that the ultra intense field might have a stabilizing effect on the atom. For short pulses we find almost complete ionization as the field strength increases.Comment: 34 pages Late

On the Influence of Pulse Shapes on Ionization Probability

We investigate analytical expressions for the upper and lower bounds for the ionization probability through ultra-intense shortly pulsed laser radiation. We take several different pulse shapes into account, including in particular those with a smooth adiabatic turn-on and turn-off. For all situations for which our bounds are applicable we do not find any evidence for bound-state stabilization.Comment: 21 pages LateX, 10 figure

Distribution of Husimi Zeroes in Polygonal Billiards

The zeroes of the Husimi function provide a minimal description of individual quantum eigenstates and their distribution is of considerable interest. We provide here a numerical study for pseudo- integrable billiards which suggests that the zeroes tend to diffuse over phase space in a manner reminiscent of chaotic systems but nevertheless contain a subtle signature of pseudo-integrability. We also find that the zeroes depend sensitively on the position and momentum uncertainties with the classical correspondence best when the position and momentum uncertainties are equal. Finally, short range correlations seem to be well described by the Ginibre ensemble of complex matrices.Comment: includes 13 ps figures; Phys. Rev. E (in press