Unexpected features of e+e-->ppbar and e+e-->lambda-lambdabar cross sections near threshold

Unexpected features of the BaBar data on e+e- in baryon-antibaryon cross sections are discussed. These data have been collected, with unprecedented accuracy, by means of the initial state radiation technique, which is particularly suitable in giving good acceptance and energy resolution at threshold. A striking feature observed in the BaBar data is the non-vanishing cross section at threshold for all these processes. This is the expectation due to the Coulomb enhancement factor acting on a charged fermion pair. In the case of e+e- in proton-antiproton it is found that Coulomb final state interactions largely dominate the cross section and the form factor is |G^p(4M^2_p)|~1, which could be a general feature for baryons. In the case of neutral baryons an interpretation of the non-vanishing cross section at threshold is suggested, based on quark electromagnetic interaction and taking into account the asymmetry between attractive and repulsive Coulomb factors. Besides strange baryon cross sections are compared to U-spin invariance predictions.Comment: 12 pages, 11 figure

Independent tuning of excitonic emission energy and decay time in single semiconductor quantum dots

Independent tuning of emission energy and decay time of neutral excitons confined in single self-assembled In(Ga)As/GaAs quantum dots is achieved by simultaneously employing vertical electric fields and lateral biaxial strain fields. By locking the emission energy via a closed-loop feedback on the piezoelectric actuator used to control the strain in the quantum dot, we continuously decrease the decay time of an exciton from 1.4 to 0.7 ns. Both perturbations are fully electrically controlled and their combination offers a promising route to engineer the indistinguishability of photons emitted from spatially separated single photon sources. © 2017 Author(s)

Independent tuning of excitonic emission energy and decay time in single semiconductor quantum dots

Independent tuning of emission energy and decay time of neutral excitons confined in single self-assembled In(Ga)As/GaAs quantum dots is achieved by simultaneously employing vertical electric fields and lateral biaxial strain fields. By locking the emission energy via a closed-loop feedback on the piezoelectric actuator used to control the strain in the quantum dot, we continuously decrease the decay time of an exciton from 1.4 to 0.7 ns. Both perturbations are fully electrically controlled and their combination offers a promising route to engineer the indistinguishability of photons emitted from spatially separated single photon sources

Slow and fast single photons from a quantum dot interacting with the excited state hyperfine structure of the Cesium D1-line

Hybrid interfaces between distinct quantum systems play a major role in the implementation of quantum networks. Quantum states have to be stored in memories to synchronize the photon arrival times for entanglement swapping by projective measurements in quantum repeaters or for entanglement purification. Here, we analyze the distortion of a single-photon wave packet propagating through a dispersive and absorptive medium with high spectral resolution. Single photons are generated from a single In(Ga)As quantum dot with its excitonic transition precisely set relative to the Cesium D1 transition. The delay of spectral components of the single-photon wave packet with almost Fourier-limited width is investigated in detail with a 200 MHz narrow-band monolithic Fabry-Pérot resonator. Reflecting the excited state hyperfine structure of Cesium, “slow light” and “fast light” behavior is observed. As a step towards room-temperature alkali vapor memories, quantum dot photons are delayed for 5 ns by strong dispersion between the two 1.17 GHz hyperfine-split excited state transitions. Based on optical pumping on the hyperfine-split ground states, we propose a simple, all-optically controllable delay for synchronization of heralded narrow-band photons in a quantum network

Engineering of quantum dot photon sources via electro-elastic fields

The possibility to generate and manipulate non-classical light using the tools of mature semiconductor technology carries great promise for the implementation of quantum communication science. This is indeed one of the main driving forces behind ongoing research on the study of semiconductor quantum dots. Often referred to as artificial atoms, quantum dots can generate single and entangled photons on demand and, unlike their natural counterpart, can be easily integrated into well-established optoelectronic devices. However, the inherent random nature of the quantum dot growth processes results in a lack of control of their emission properties. This represents a major roadblock towards the exploitation of these quantum emitters in the foreseen applications. This chapter describes a novel class of quantum dot devices that uses the combined action of strain and electric fields to reshape the emission properties of single quantum dots. The resulting electro-elastic fields allow for control of emission and binding energies, charge states, and energy level splittings and are suitable to correct for the quantum dot structural asymmetries that usually prevent these semiconductor nanostructures from emitting polarization-entangled photons. Key experiments in this field are presented and future directions are discussed.Comment: to appear as a book chapter in a compilation "Engineering the Atom-Photon Interaction" published by Springer in 2015, edited by A. Predojevic and M. W. Mitchel

Metal - Insulator transition driven by vacancy ordering in GeSbTe phase change materials

Phase Change Materials (PCMs) are unique compounds employed in non-volatile random access memory thanks to the rapid and reversible transformation between the amorphous and crystalline state that display large differences in electrical and optical properties. In addition to the amorphousto-crystalline transition, experimental results on polycrystalline GeSbTe alloys (GST) films evidenced a Metal-Insulator Transition (MIT) attributed to disorder in the crystalline phase. Here we report on a fundamental advance in the fabrication of GST with out-of-plane stacking of ordered vacancy layers by means of three distinct methods: Molecular Beam Epitaxy, thermal annealing and application of femtosecond laser pulses. We assess the degree of vacancy ordering and explicitly correlate it with the MIT. We further tune the ordering in a controlled fashion attaining a large range of resistivity. Employing ordered GST might allow the realization of cells with larger programming windows

Validity and reproducibility of a semi-quantitative food frequency questionnaire in Spanish preschoolers - The SENDO project

Introduction: nowadays, it is important to determine whether food frequency questionnaires (FFQ) are valid tools to collect information on usual diet in children. Objective: we evaluated the reproducibility and validity of the semi-quantitative FFQ used in a Spanish cohort of children aged 4-7 years. Methods: to explore its reproducibility, parents filled a 138-item FFQ at baseline (FFQ-0) and then one year later (FFQ-1). To explore its validity, the FFQ-1 was compared with four weighed 3-day dietary records (DRs) that were used as standard of reference. To estimate associations we calculated deattenuated Pearson’s correlation coefficients to correct for season-to-season variability, and the Bland-Altman index. We also calculated the weighted kappa index and assessed participant’s gross misclassification across quintiles. We analyzed data from 67 (for reproducibility) and 37 (for validity) children aged 4-7 years old, recruited by the pilot study of the SENDO project. Results: regarding reproducibility, we found mean Bland-Altman indexes of 0-10.45 % for nutrients and 1.49 %-10.45 % for foods. The adjusted r ranged between 0.29 and 0.71, and between 0.27 and 0.74 for nutrients and foods, respectively. Regarding validity, we found mean Bland-Altman indexes of 0 %-16.22 % and 0 %-10.81 % for nutrients and for food groups, respectively. The deattenuated r ranged between 0.38 and 0.81 for nutrients, and between 0.53 and 0.68 for foods. The weighted kappa index for agreement across quintiles ranged from 54.1 to 85.1 for nutrients, and from 55.4 to 78.4 for food groups. Conclusions: our results showed acceptable levels of both reproducibility and validity, and that the ad-hoc developed FFQ is a valid tool for assessing usual diet in Spanish preschoolers.Introducción: es importante determinar si los cuestionarios de frecuencia de consumo de alimentos (CFCA) son herramientas válidas para recopilar información sobre la dieta habitual en los niños. Objetivo: evaluar la reproducibilidad y validez del CFCA semi-cuantitativo de una cohorte española de niños de 4 a 7 años. Métodos: en total se estudiaron 67 (para reproducibilidad) y 37 (para validez) niños de 4 a 7 años de edad del estudio piloto del proyecto SENDO. Para explorar la reproducibilidad, los padres cumplimentaron el CFCA basalmente (CFCA-0) y al año (CFCA-1). Para explorar la validez, el CFCA-1 se comparó con cuatro registros dietéticos (DR) pesados de 3 días. Calculamos coeficientes de correlación de Pearson desatenuados para corregir la variabilidad inter-estacional, y el índice de Bland-Altman. El índice kappa ponderado permitió evaluar la clasificación errónea de los participantes entre quintiles. Resultados: respecto a la reproducibilidad, encontramos índices promedio de Bland-Altman de 0-10,45 % para los nutrientes y de 1,49-10,45 % para los alimentos. La r ajustada varió entre 0,29 y 0,71, y entre 0,27 y 0,74 para nutrientes y alimentos, respectivamente. En cuanto a la validez, encontramos índices promedio de Bland-Altman de 0-16,22 % y 0-10,81 % para nutrientes y alimentos, respectivamente. La r desatenuada osciló entre 0,38 y 0,81 para los nutrientes y entre 0,53 y 0,68 para los alimentos. El índice kappa ponderado para el acuerdo entre quintiles varió entre 54,1 y 85,1 para los nutrientes y entre 55,4 y 78,4 para los grupos de alimentos. Conclusiones: nuestros resultados mostraron niveles aceptables tanto de reproducibilidad como de validez. El FFQ desarrollado ad hoc es una herramienta válida para evaluar nutrientes y alimentos en preescolares españoles