Quantum Noise in Multipixel Image Processing

We consider the general problem of the quantum noise in a multipixel measurement of an optical image. We first give a precise criterium in order to characterize intrinsic single mode and multimode light. Then, using a transverse mode decomposition, for each type of possible linear combination of the pixels' outputs we give the exact expression of the detection mode, i.e. the mode carrying the noise. We give also the only way to reduce the noise in one or several simultaneous measurements.Comment: 8 pages and 1 figur

Three-Nucleon Continuum by means of the Hyperspherical Adiabatic Method

This paper investigates the possible use of the Hyperspherical Adiabatic basis in the description of scattering states of a three-body system. In particular, we analyze a 1+2 collision process below the three-body breakup. The convergence patterns for the observables of interest are analyzed by comparison to a unitary equivalent Hyperspherical Harmonic expansion. Furthermore, we compare and discuss two different possible choices for describing the asymptotic configurations of the system, related to the use of Jacobi or hyperspherical coordinates. In order to illustrate the difficulties and advantages of the approach two simple numerical applications are shown in the case of neutron-deuteron scattering at low energies using s-wave interactions. We found that the optimization driven by the Hyperspherical Adiabatic basis is not as efficient for scattering states as in bound state applications.Comment: 29 pages, 5 figures, accepted for publication in Few-Body Systems (in press

Direct Production of Tripartite Pump-Signal-Idler Entanglement in the Above-Threshold Optical Parametric Oscillator

We calculate the quantum correlations existing among the three output fields (pump, signal, and idler) of a triply resonant non-degenerate Optical Parametric Oscillator operating above threshold. By applying the standard criteria [P. van Loock and A. Furusawa, Phys. Rev. A 67, 052315 (2003)], we show that strong tripartite continuous-variable entanglement is present in this well-known and simple system. Furthermore, since the entanglement is generated directly from a nonlinear process, the three entangled fields can have very different frequencies, opening the way for multicolored quantum information networks.Comment: 4 pages, 3 figure

Valoración y clasificación de la irregularidad interanual: Aplicación en la cuenca del Ebro.

La irregularidad interanual es una de las principales características que definen el comportamiento de los ríos. Su magnitud debe ser tenida en cuenta en la gestión de los caudales de los cursos fluviales. Es, por tanto, conveniente establecer una clasificación de esta irregularidad interanual de los ríos, a través de una mecánica simple. El objetivo de este trabajo es elaborar una propuesta de categorización de la irregularidad interanual en clases o tipos bien definidos y contrastados. Previamente hay que determinar un método sencillo y riguroso para obtener los valores de irregularidad interanual, a partir de las series de datos de aforos. La aplicación de esta propuesta en los ríos de la Cuenca del Ebro permite establecer la presencia de 5 niveles o categorías de irregularidad interanual, con una distribución marcada por diferentes factores geográficos. En ella se aprecia un marcado contraste entre los ríos de las márgenes izquierda y derecha del Ebro. The interannual variation of the water discharge is one of the main characteristics that defines the behavior of rivers. The magnitude of this irregularity must be taken into account in managing the flow of watercourses. Therefore, it is desirable to establish a classification of this interannual variation of rivers, by using simple procedures. The aim of this work is to develope a proposal of categorization of the interannual variation in well defined and contrasted types. First of all, it is necessary to determine a simple and accurate method to obtain interannual irregularity values, from the series of traffic counts data. Thanks to the implementation of this proposal in the Ebro's Basin rivers, it is possible to distinguish between 5 levels or categories of the interannual variation, with a geographical distribution marked by different factors. This shows a strong contrast between the rivers on the left and right banks of the Ebro. Keywords: River; interannual variability; river regimes; Ebro basin

Determination of two-body potentials from n-body spectra

We show how the two-body potential may be uniquely determined from n-body spectra where the hypercentral approximation is valid. We illustrate this by considering an harmonic oscillator potential which has been altered by changing the energy or normalisation constant of the ground state of the n-body system and finding how this modifies the two-body potential. It is shown that with increasing number of particles the spectrum must be known more precisely to obtain the two-body potential to the same degree of accuracy.Comment: 13 pages of text (LATEX), 3 figures (not included, available from authors), NIKHEF-93-P

From spin-Peierls to superconductivity: (TMTTF)_2PF_6 under high pressure

The nature of the attractive electron-electron interaction, leading to the formation of Cooper-pairs in unconventional superconductors has still to be fully understood and is subject to intensive research. Here we show that the sequence spin-Peierls, antiferromagnetism, superconductivity observed in (TMTTF)_2PF_6 under pressure makes the (TM)_2X phase diagram universal. We argue that the suppression of the spin-Peierls transition under pressure, the close vicinity of antiferromagnetic and superconducting phases at high pressure as well as the existence of critical antiferromagnetic fluctuations above T_c strongly support the intriguing possibility that the interchain exchange of antiferromagnetic fluctuations provides the pairing mechanism required for bound charge carriers.Comment: 4 pages, revtex, 4 figures (jpeg,eps,png