title: Multistage entanglement swapping.
abstract: We report an experimental demonstration of entanglement swapping over two quantum stages. By successful realizations of two cascaded photonic entanglement swapping processes, entanglement is generated and distributed between two photons, that originate from independent sources and do not share any common past. In the experiment we use three pairs of polarization entangled photons and conduct two Bell-state measurements: one between the first and second pair, and one between the second and third pair. This results in projecting the remaining two outgoing photons from pair 1 and 3 into an entangled state, as characterized by an entanglement witness. The experiment represents an important step towards a full quantum repeater where multiple entanglement swapping is a key ingredient.
authors.affiliation: Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Philosophenweg 12, 69120 Heidelberg, Germany.
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Goebel
authors.forename: Claudia
authors.initials: C
authors.lastname: Wagenknecht
authors.forename: Qiang
authors.initials: Q
authors.lastname: Zhang
authors.forename: Yu-Ao
authors.initials: YA
authors.lastname: Chen
authors.forename: Kai
authors.initials: K
authors.lastname: Chen
authors.forename: Jörg
authors.initials: J
authors.lastname: Schmiedmayer
authors.forename: Jian-Wei
authors.initials: JW
authors.lastname: Pan