Spontaneous patterns in coherently driven polariton microcavities

We consider a polariton microcavity resonantly driven by two external lasers which simultaneously pump both lower and upper polariton branches at normal incidence. In this setup, we study the occurrence of instabilities of the pump-only solutions towards the spontaneous formation of patterns. Their appearance is a consequence of the spontaneous symmetry breaking of translational and rotational invariance due to interaction induced parametric scattering. We observe the evolution between diverse patterns which can be classified as single-pump, where parametric scattering occurs at the same energy as one of the pumps, and as two-pump, where scattering occurs at a different energy. For two-pump instabilities, stripe and chequerboard patterns become the dominant steady-state solutions because cubic parametric scattering processes are forbidden. This contrasts with the single-pump case, where hexagonal patterns are the most common arrangements. We study the possibility of controlling the evolution between different patterns. Our results are obtained within a linear stability analysis and are confirmed by finite size full numerical calculations.Comment: 15 pages, 9 figure

Silicon purification using a Cu-Si alloy source

Production of 99.9999% pure silicon from 98% pure metallurgical grade (MG) silicon by a vapor transport filtration process (VTP) is described. The VTF process is a cold wall version of an HCl chemical vapor transport technique using a Si:Cu3Si alloy as the silicon source. The concentration, origin, and behavior of the various impurities involved in the process were determined by chemically analyzing alloys of different purity, the slag formed during the alloying process, and the purified silicon. Atomic absorption, emission spectrometry, inductively coupled plasma, spark source mass spectrometry, and secondary ion mass spectroscopy were used for these analyses. The influence of the Cl/H ratio and the deposition temperature on the transport rate was also investigated

All-optical non-demolition measurement of single-hole spin in a quantum-dot molecule

We propose an all-optical scheme to perform a non-demolition measurement of a single hole spin localized in a quantum-dot molecule. The latter is embedded in a microcavity and driven by two lasers. This allows to induce Raman transitions which entangle the spin state with the polarization of the emitted photons. We find that the measurement can be completed with high fidelity on a timescale of 100 ps, shorter than the typical T2. Furthermore, we show that the scheme can be used to induce and observe spin oscillations without the need of time-dependent magnetic fields

Double Pion Photoproduction in Nuclei

The inclusive A(gamma,pi+ pi-)X reaction is studied theoretically. A sizeable enhancement of the cross section is found, in comparison with the scaling of the deuteron cross section (sigma_deuteron * A/2). This enhancement is due to the modifications in the nuclear medium of the gamma N ----> pi pi N amplitude and the pion dispersion relation. The enhancement is found to be bigger than the one already observed in the (pi,pi pi) reaction in nuclei.Comment: 11 pages, 7 figures (figures available from authors); TeX, Version 3.141 [PD VMS 3.4/CERN 1.0

Innovación, docencia e investigación como cambio y transformación en el ámbito de la publicación universitaria: International Journal of Educational Research and Innovation

-Artículo revisado por pare

Spin Information from Vector-Meson Decay in Photoproduction

For the photoproduction of vector mesons, all single and double spin observables involving vector meson two-body decays are defined consistently in the $\gamma N$ center of mass. These definitions yield a procedure for extracting physically meaningful single and double spin observables that are subject to known rules concerning their angle and energy evolution. As part of this analysis, we show that measuring the two-meson decay of a photoproduced $\rho$ or $\phi$ does not determine the vector meson's vector polarization, but only its tensor polarization. The vector meson decay into lepton pairs is also insensitive to the vector meson's vector polarization, unless one measures the spin of one of the leptons. Similar results are found for all double spin observables which involve observation of vector meson decay. To access the vector meson's vector polarization, one therefore needs to either measure the spin of the decay leptons, make an analysis of the background interference effects or relate the vector meson's vector polarization to other accessible spin observables.Comment: 22 pages, 3 figure

Estrategias para la formación e innovación universitarias en tiempos de pandemia

In this article, I set out to demonstrate the need for a student-centred model, which would enable students, through the proper effective use of ICT, to develop critical awareness, creativity, and knowledge. However, this process must be mediated by a teacher who is competent in the use of ICT and knows how to get the most out of them, so that teaching becomes more than merely a "container" of content. This paper presents a brief chronological overview of the events of the pandemic and its most immediate consequences of moving from face-to-face teaching to online delivery in such a short space of time. Finally, it will review the actions carried out by the Universidad Pablo de Olavide, in Seville, in the field of training and innovation.En este artículo he tratado de evidenciar la necesidad de que se opte de manera definitiva por un modelo centrado en el alumno de manera que sean ellos los que a través de las TIC y el buen uso de éstas se conviertan en personas con sentido crítico, con creatividad y conocimiento. Pero en este proceso se hace fundamental la mediación del docente que debe conocer no ya las TIC sino cómo se le puede sacar el máximo partido para que la docencia no sea un mero "contenedor" de contenidos. Se expondrá una breve reseña cronológica de los acontecimientos de la pandemia y las consecuencias más inmediatas al pasar de una enseñanza de carácter presencial a otra online en tan poco tiempo. Y finamente se reseñarán las actuaciones en el ámbito de la formación e innovación llevada a cabo dese la Universidad Pablo de Olavide de Sevilla (UPO).Universidad Pablo de Olavid