Matias El ruben

We present an efficient method to control the spatial modes of entangled photons produced through SPDC process. Bi-photon beam propagation is controlled by a deformable mirror that shapes a 404nm CW diode laser pump interacting with a nonlinear BBO type-I crystal. Thanks to adaptive optical system, the propagation of 808nm SPDC light produced is optimized over a distance of 2m. The whole system optimization is carried out by a feedback between deformable mirror action and entangled photon coincidence counts.

The purpose of the work was to investigate the propagation of single photon beams over the inter-island link, and in particular between a transmitter on the roof of the Jacob Kapteyn Telescope at ORM, La Palma, and the ESA-Optical Ground Station at Izana, Tenerife as receiver. Indeed, the study of the free-space propagation of quantum correlations is necessary for any future application of quantum communication aiming to connect two remote locations. The problem related to the free-space propagation is represented by the atmospheric turbulence that acts as a temporal and spatial variation of the air refraction index. A turbulent channel acts as an increment of the losses on the transmitted photons due to beam wandering of the beam centroid or to scintillation, increasing the role of the noise.