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.Comment: To appear in Journal of Physics: Condensed Matte

Crossover between the Dense Electron-Hole Phase and the BCS Excitonic Phase in Quantum Dots

Second order perturbation theory and a Lipkin-Nogami scheme combined with an exact Monte Carlo projection after variation are applied to compute the ground-state energy of $6\le N\le 210$ electron-hole pairs confined in a parabolic two-dimensional quantum dot. The energy shows nice scaling properties as N or the confinement strength is varied. A crossover from the high-density electron-hole phase to the BCS excitonic phase is found at a density which is roughly four times the close-packing density of excitons.Comment: Improved variational and projection calculations. 17 pages, 3 ps figures. Accepted for publication in Int. J. Mod. Phys.

Coulomb correlations of a few body system of spatially separated charges

A Hartree-Fock and Hartree-Fock-Bogoliubov study of a few body system of spatially separated charge carriers was carried out. Using these variational states, we compute an approximation to the correlation energy of a finite system of electron-hole pairs. This energy is shown as a function of the Coulomb coupling and the interplane distance. We discuss how the correlation energy can be used to theoretically determine the formation of indirect excitons in semiconductors which is relevant for collective phenomena such as Bose-Einstein condensation (BEC).Comment: Conference EDISON16 (2009), 4 page

Effects of Coulomb interactions on the splitting of luminescence lines

We study the splitting between the right-hand and left-hand circularly polarized luminescence lines in a quantum dot under relatively weak confinement regime and resonant high-power excitation. When the dot is populated with an even number of electron-hole pairs (biexciton and higher excitations), the splitting measures basically the Zeeman energy. However, in the odd number of pairs case, we have, in addition to the Zeeman and Overhauser shifts, a contribution to the splitting coming from Coulomb interactions. This contribution is of the order of a few meV, and shows distinct signatures of shell-filling in the quantum dot.Comment: Submitted for publicatio

Photon emission as a source of coherent behaviour 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 to this statement

¿Por qué hacer ciencia (básica) en Colombia?: la visión muy personal de un “científico” colombiano

Generalmente en el salón de clases, frente a estudiantes de primer semestre de Física o Astronomía, o estudiantes de quinto semestre de Mecánica clásica o Física matemática, o aún frente a estudiantes que están finalizado sus carreras o incluso en los se-minarios “Landau o alemanes” con mis estudiantes de maestría y doctorado, intento ser optimista frente al reto que tienen de desa-rrollarse como científicos en un país como Colombia. Intento con-vencerlos desde la pasión por el conocimiento de la importancia que tiene hacer ciencia, del valor singular que como ciudadanos de estas tierras macondianas tiene el de participar de una aventura cultural global del conocimiento, intento convencerlos de que po-demos alcanzar las más altas cumbres sin olvidar nuestro contexto y nuestra historia.Generalmente en el salón de clases, frente a estudiantes de primer semestre de Física o Astronomía, o estudiantes de quinto semestre de Mecánica clásica o Física matemática, o aún frente a estudiantes que están finalizado sus carreras o incluso en los se-minarios “Landau o alemanes” con mis estudiantes de maestría y doctorado, intento ser optimista frente al reto que tienen de desa-rrollarse como científicos en un país como Colombia. Intento con-vencerlos desde la pasión por el conocimiento de la importancia que tiene hacer ciencia, del valor singular que como ciudadanos de estas tierras macondianas tiene el de participar de una aventura cultural global del conocimiento, intento convencerlos de que po-demos alcanzar las más altas cumbres sin olvidar nuestro contexto y nuestra historia

Micropillar resonator in a magnetic field: Zero and Finite temperature cases

In this work, we present a theoretical study of a quantum dot-microcavity system which includes a constant magnetic field in the growth direction of the micropillar. First, we study the zero temperature case by means of a selfconsistent procedure with a trial function composed by a coherent photon field and a BCS function for the electron-hole pairs. The dependence of the ground-state energy on the magnetic field and the number of polaritons is found. We show that the magnetic field can be used as a control parameter of the photon number, and we make explicit the scaling of the total energy with the number of polaritons. Next, we study this problem at finite temperatures and obtain the scaling of the critical temperature with the number of polaritons.Comment: "Paper presented in PLMCN7. To appear in Superlattices and Microstructures

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 ten 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.Comment: 4 pages, 4 fig

Environmental genomics of "Haloquadratum walsbyi" in a saltern crystallizer indicates a large pool of accessory genes in an otherwise coherent species

BACKGROUND: Mature saturated brine (crystallizers) communities are largely dominated (>80% of cells) by the square halophilic archaeon "Haloquadratum walsbyi". The recent cultivation of the strain HBSQ001 and thesequencing of its genome allows comparison with the metagenome of this taxonomically simplified environment. Similar studies carried out in other extreme environments have revealed very little diversity in gene content among the cell lineages present. RESULTS: The metagenome of the microbial community of a crystallizer pond has been analyzed by end sequencing a 2000 clone fosmid library and comparing the sequences obtained with the genome sequence of "Haloquadratum walsbyi". The genome of the sequenced strain was retrieved nearly complete within this environmental DNA library. However, many ORF's that could be ascribed to the "Haloquadratum" metapopulation by common genome characteristics or scaffolding to the strain genome were not present in the specific sequenced isolate. Particularly, three regions of the sequenced genome were associated with multiple rearrangements and the presence of different genes from the metapopulation. Many transposition and phage related genes were found within this pool which, together with the associated atypical GC content in these areas, supports lateral gene transfer mediated by these elements as the most probable genetic cause of this variability. Additionally, these sequences were highly enriched in putative regulatory and signal transduction functions. CONCLUSION: These results point to a large pan-genome (total gene repertoire of the genus/species) even in this highly specialized extremophile and at a single geographic location. The extensive gene repertoire is what might be expected of a population that exploits a diverse nutrient pool, resulting from the degradation of biomass produced at lower salinities