Abstract:
We suggest and demonstrate a novel source of two-photon multipartite entangled states which exploits the transverse spatial structure of spontaneous parametric downconversion together with a programmable spatial light modulator (SLM). The 1D SLM is used to perform polarization entanglement purification and to realize arbitrary phase-gates between polarization and momentum degrees of freedom of photons. We experimentally demonstrate our scheme by generating two-photon three qubit linear cluster states with high fidelity using a diode laser pump with a limited coherence time and power on the crystal as low as 2.5$mW.

Abstract:
We suggest and demonstrate an all-optical experimental setup to observe and engineer entanglement oscillations of a pair of polarization qubits in a non-Markovian channel. We generate entangled photon pairs by spontaneous parametric downconversion (SPDC), and then insert a programmable spatial light modulator in order to impose a polarization dependent phase-shift on the spatial domain of the SPDC output and to create an effective non-Markovian environment. Modulation of the enviroment spectrum is obtained by inserting a spatial grating on the signal arm. In our experiment, programmable oscillations of entanglement are achieved, with the maximally revived state that violates Bell's inequality by 17 standard deviations.

Abstract:
We suggest and demonstrate a scheme to compensate spatial and spectral decoherence effects in the generation of polarization entangled states by type-I parametric downconversion. In our device a programmable spatial light modulator imposes a polarization dependent phase-shift on different spatial sections of the overall downconversion output and this effect is exploited to realize an effective purification technique for polarization entanglement.

Abstract:
We address the problem of achieving a random laser with a cloud of cold atoms, in which gain and scattering are provided by the same atoms. In this system, the elastic scattering cross-section is related to the complex atomic polarizability. As a consequence, the random laser threshold is expressed as a function of this polarizability, which can be fully determined by spectroscopic measurements. We apply this idea to experimentally evaluate the threshold of a random laser based on Raman gain between non-degenerate Zeeman states and find a critical optical thickness on the order of 200, which is within reach of state-of-the-art cold-atom experiments.

Abstract:
Let X be a projective manifold, of dimension n≥3, and L a very ample line bundle on X. In this paper we investigate the pairs (X,L) with the following property: there exists a transversal intersection of n-1 members of |L| which is a smooth d-gonal curve (d=3,4). We prove, under suitable assumptions, that n≤4 or 5 (resp. if d=3 or 4) and (X,L) is a fibration over P1 with genera; fibre a rational cubic (resp. quartic) scroll.

Abstract:
Resumo: A Teoria das Representa es Sociais se mostra, claramente, como uma vertente sociológica da Psicologia Social. O pensador Durkheim, com o conceito de “representa o coletiva”, influenciou, de maneira acentuada, os estudos modernos sobre as representa es. Serge Moscovici, debru ando-se sobre a quest o das representa es, denomina-as de “sociais”, cunhando o termo “representa es sociais”. Essa conceitua o se deve à necessidade prática e teórica de destacar a importancia de determinados elementos na conforma o das representa es nas complexas sociedades modernas: comunica o, acelerada dinamica social e heterogeneidade.

Abstract:
L’article propose un aper u du vaudou Tchamba. Ce culte évoque à travers la pratique rituelle, la mémoire des hommes achetés comme esclaves. L’étude des formes de mémoire non verbales permet de déceler des traces de la mémoire de l’esclavage explicitant un sentiment diffus de conscience. à travers l’étude de la possession dans le culte Tchamba, on peut voir comment parallèlement à la narration historique, il y a d’autres fa ons de raconter et se remémorer l’histoire.

Abstract:
Atoms can scatter light and they can also amplify it by stimulated emission. From this simple starting point, we examine the possibility of realizing a random laser in a cloud of laser-cooled atoms. The answer is not obvious as both processes (elastic scattering and stimulated emission) seem to exclude one another: pumping atoms to make them behave as amplifier reduces drastically their scattering cross-section. However, we show that even the simplest atom model allows the efficient combination of gain and scattering. Moreover, supplementary degrees of freedom that atoms offer allow the use of several gain mechanisms, depending on the pumping scheme. We thus first study these different gain mechanisms and show experimentally that they can induce (standard) lasing. We then present how the constraint of combining scattering and gain can be quantified, which leads to an evaluation of the random laser threshold. The results are promising and we draw some prospects for a practical realization of a random laser with cold atoms.

Abstract:
Let U(r) be the moduli space of rank r vector bundles with trivial determinant on a smooth curve of genus 2. The map theta_r: U(r) -> |r Theta|, which associates to a general bundle its theta divisor, is generically finite. In this paper we give a geometric interpretation of the generic fibre of theta_r.

Abstract:
Let $C$ be an algebraic smooth complex genus $g>1$ curve. The object of this paper is the study of the birational structure of the coarse moduli space $U_C(r,0)$ of semi-stable rank r vector bundles on $C$ with degree 0 determinant and of its moduli subspace $SU_C(r)$ given by the vector bundles with trivial determinant. Notably we prove that $U_C(r,0)$ (resp. $SU_C(r)$) is birational to a fibration over the symmetric product $C^(rg)$ (resp. over $P^{(r-1)g}$) whose fibres are GIT quotients $(P^{r-1})^{rg}//PGL(r)$. In the cases of low rank and genus our construction produces families of classical modular varieties contained in the Coble hypersurfaces.