Boris A. Rodriguez

The electron g factor of cylindrical GaAs?Ga1?xAlxAs quantum well wires under magnetic fields applied along the wire axis

The effects of confinement and magnetic fields on the effective electron Land? g factor of GaAs?Ga1?xAlxAs cylindrical quantum well wires are studied. Calculations were carried out via the Ogg?McCombe effective Hamiltonian which is used to describe the non-parabolicity and anisotropy effects on the electron states in the conduction band. The applied magnetic field is taken along the wire axis, and the Schr?dinger equation corresponding to electron spin projections parallel and antiparallel to the magnetic field is solved by using an expansion of the electron wavefunctions in terms of two-dimensional harmonic oscillator wavefunctions. Calculations for the electron factor in GaAs?Ga1?xAlxAs cylindrical quantum well wires are compared with results from previous theoretical work. Moreover, the present results clearly indicate the importance of taking into account the non-parabolicity/anisotropy of the conduction band if one is interested in a quantitative understanding of the electron g factor in GaAs?Ga1?xAlxAs quantum well wires.

Characterization of dynamical regimes and entanglement sudden death in a microcavity quantum dot system

The relation between the dynamical regimes (weak and strong coupling) and entanglement for a dissipative quantum dot microcavity system is studied. In the framework of a phenomenological temperature model an analysis in both temporal (population dynamics) and frequency domain (photoluminescence) is carried out in order to identify the associated dynamical behavior. The Wigner function and concurrence are employed to quantify the entanglement in each regime. We find that sudden death of entanglement is a typical characteristic of the strong coupling regime.

Variability of extreme events in the Colombian Pacific and Caribbean catchment basins

This paper analyses the behavior of extreme events of surface precipitation and temperature inside the Pacific and Caribbean Catchment Basins in Colombia using several datasets such as observations, reconstructed data, NCEP-NCAR and ERA-40 reanalyses and data from the regional model REMO. We use an extreme value method that selects the time series excesses over a nonstationary threshold and adjusts them to a generalized Pareto distribution. The goodness of fit is evaluated through a test that includes the Cramer–von Mises, Kolmogorov–Smirnov and Anderson–Darling statistics and the p values generated by parametric bootstrap resampling. The test not only evaluates the goodness of fit but also the threshold choice. The parameters are presented in maps that allow recognition of the features of the extreme behaviour inside the catchment basins, and differences and similarities between them. Maps of return periods for the maximum extreme events are also presented. A strong influence of the El Niño–Southern oscillation on the extreme events of both temperature and precipitation is found in the two catchment basins.

Density operator of a system pumped with polaritons: a Jaynes?Cummings-like approach

We investigate the effects of considering two different incoherent excitation mechanisms on microcavity quantum dot systems modeled using the Jaynes-Cummings Hamiltonian. When the system is incoherently pumped with polaritons it is able to sustain a large number of photons inside the cavity with Poisson-like statistics in the stationary limit, and it also leads to a separable exciton-photon state. We also investigate the effects of both types of pumpings (excitonic and polaritonic) in the emission spectrum of the cavity. We show that the polaritonic pumping considered here is unable to modify the dynamical regimes of the system at variance with the excitonic pumping. Finally, we obtain a closed form expression for the negativity of the density matrices that the quantum master equation considered here generates.

Photon emission as a source of coherent behavior of polaritons.

We show that the combined effect of photon emission and Coulomb interactions may drive an exciton-polariton system towards a dynamical coherent state, even without phonon thermalization or any other relaxation mechanism. Exact diagonalization results for a finite system (a multilevel quantum dot interacting with the lowest-energy photon mode of a microcavity) are presented in support of this statement.

A multiexcitonic quantum dot in an optical microcavity

We theoretically study the coupled modes of a medium-size quantum dot, which may confine a maximum of 10 electron–hole pairs, and a single photonic mode of an optical microcavity. Ground-state and excitation energies, exciton–photon mixing in the wave functions and the emission of light from the microcavity are computed as functions of the pair–photon coupling strength, photon detuning, and polariton number.

Dynamics of entanglement and quantum discord in the Tavis–Cummings model

We revisit the problem of the dynamics of quantum correlations in the Tavis–Cummings model. Our results show that the dynamics of entanglement and quantum discord are far from being trivial or intuitive. We find states with the same entanglement but different discord and states where the two quantifiers give opposite information about correlations at a certain time. We furthermore show that many of the dynamical features of quantum discord attributed to dissipation are already present in the exact framework and are due to the characteristic quantum nonlinearity of the model and to the choice of initial conditions. Through a comprehensive analysis of pure and mixed initial conditions, we find a fascinating range of phenomena that can be used for experimental purposes. We propose an experiment called quantum discord gates where for a given pure initial condition discord is zero or non-zero depending on the number of photons in the cavity. Given the marginal character of states with zero discord this result is not only completely counterintuitive but is also useful as a way to count photons.

Spin polarization and magneto-luminescence of confined electron-hole systems

peratures we end up with an “stable” N-pair e-h cluster in its ground state. Results for spin-up and -down densities, hole and electron spin polarizations and for the position and magnitude of the coherent luminescence peak as functions of the magnetic field and of the mean number of excitons are presented below. The theoretical framework used is a BCS-like wave function, corrected against particle number non-conservation by means of a Lipkin-Nogami procedure 9,10 . This wave function is able to reproduce the expected “Bose condensed” state in the B → ∞ limit 11,12,13 . A big basis of one-particle states is used, which includes up to 3 Landau levels and 202 states per Landau level. We consider systems with up to 40 e-h pairs.

Variability of regional atmospheric moisture over Northern South America: patterns and underlying phenomena

We evaluate the spatio-temporal variability of atmospheric moisture in northern South America. The spatial structure of moisture is discussed in seasonal and interannual time scales. We combine the principal component analysis of moisture flux divergence and the physical information flow to measure the relative influence of global climate phenomena in the leading modes of regional variability. Our results highlight the inherent complexity of spatial structure in this region due to the interaction of the Tropical Andes, the regional circulation changes related to the annual migration of the ITCZ, the low-level jet structures of regional atmospheric transport and the moisture transport from surrounding marine areas. Modes of variability related to oscillations in the tropical and extratropical Atlantic and Tropical Pacific are the most important sources of variability underlying the regional atmospheric moisture. To emphasize ENSO related variability, we propose a seasonal state classification index that unambiguously classifies the local evolution of precipitation in El Niño and La Niña years, showing the occurrence of marked differences in local moisture content in each of these phases.

Mecánica cuántica fundamental, una propuesta didáctica

Fundamental quantum mechanics (FQM) is a commented presentation of fundamental experiments and concepts of quantum mechanics, the physical theory of the quantum phenomena domain: superposition principle and quantum entanglement become the cornestone of the theoretical foundation of the quantum description. The formalism of these basic notions, for two-level systems, is presented. Also, the quantum measurement problem is stated through the discussion of the ideas of probability, evolution (dynamics) and measurement. Finally, this theoretical construction is contextualized in emblematic experiments of the quantum domain: the two slit experiment, the Stern-Gerlach experiment and the Mach-Zehnder interferometer, and in technological applications, such as quantum teleportation and quantum cryptography. Besides, the FQM is a pedagogical proposal, formed by six didactic sequences, for high school teachers and students.