title: Observation of a nonlocal optical vortex.
abstract: We report the observation of an optical vortex in the correlations of photons produced from spontaneous parametric down-conversion. The singularity appears in a nonlocal coordinate plane consisting of 1 degree of freedom of each photon.
authors: Instituto de Física, Universidade Federal de Goiás, GO 74.001-970, Brazil.
authors: R M
authors: RM
authors: Gomes
authors: A
authors: A
authors: Salles
authors: F
authors: F
authors: Toscano
authors: P H Souto
authors: PH
authors: Ribeiro
authors: S P
authors: SP
authors: Walborn