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Seminário do grupo de Óptica e Informação Quântica

Data: Sexta-Feira 11/11/2011 Sala A5-01, 11h

Palestrante: Sebastião de Pádua (UFMG)

Título: Quantum information with photonic qudits.

Resumo: We present in this talk the results of recent experiments with photonic entangled qudits. Photonic entangled qudits are generated by using spontaneous parametric down conversion (SPDC) and multi-slits. In one of the experiments, a photon pair created by type I SPDC cross a three slits array producing photons in a two-entangled spatial qutrit state when the pump beam is focused at the array plane. We study the experimental reconstruction of the entangled state of the two qutrits. The state of the spatial entangled qutrits are reconstructed with the help of symmetric informationally complete positive operator valued measurement (SIC-POVM). The measurement operators involved in this process are performed using a spatial light modulator. In a second experiment a quasi-phase matching type II PPKTP crystal is pumped by a pulsed laser and one or two simultaneous pairs are generatedallowing to produce two copies of two qutrits or two ququarts states. In this set up four photons can be generated.In order to generate qudits we used the multiple-slit implementation. Using triple and quadruple slits we produced, respectively qutrits and ququarts states in which the quantum correlations between the two photons of each pair were manipulated by an optical system  placed between the crystal and the slits.  By projecting either the near or far field of the crystal onto the slits, the optical system changed the characteristics of the biphoton amplitude function and allowed us to obtain both states with very high entanglement, in the case of the near field, or very low entanglement, in the case of the far field. Interference maps between photons of the same pair and from diferent pairs allows us to reconstruct the generated states under some assumptions and calculate its entanglement.