arXiv2003
A novel ultrabright parametric source of polarization entangled photon pairs with striking spatial characteristics is reported. The distribution of the output electromagnetic k-modes excited by Spontaneous Parametris Down Conversion and coupled to the output detectors can be very broad. It could coincide with the full set of phase-matched excited modes, at least in principle. In this case a relevant conditional quasi-pure output state should be realized. By these (approximate) states realized over a full Entanglement-Ring output distribution, the non local properties of the generated entanglement has been tested by standard Bell measurements and by Ou-Mandel interferometry. A novel ''mode-patchwork'' technique based on the quantum superposition principle is adopted to synthesize in a straightforward and reliable way any kind of mixed-states, of large conceptual and technological interest in modern Quantum Information. Tunable Werner states and Maximally Entangled Mixed States (MEMS) have indeed been created by the new technique and investigated by quantum tomography. A thorough study of the entropic and nonlocal properties of these states has been undertaken experimentally and theoretically, by a unifying variational approach.