Characterizing entanglement in qubits created with spatially correlated twin photons.

L. Neves, G. Lima, E. J. S. Fonseca, L. Davidovich and S. Pádua
PHYSICAL REVIEW A 76, 32314 (2007)


We characterize entanglement in two-qubit pure states encoded in transverse momenta of twin photons
obtained from spontaneous parametric down-conversion. Two alternate methods are employed: i measurement
of conditional interference patterns and ii measurement of the marginal probability that yields the
single-photon interference pattern. Both methods are local with classical communication and rely on Schmidt
decomposition of the quantum state, which is generated by letting the photons propagate through an appropriate
lens system. In both cases we can obtain the concurrence either through the Schmidt coefficients in the first
method or directly relating the concurrence to the visibility of the interference pattern in the second one.

DOI: 10.1103/PhysRevA.76.032314