title: Experimental observation of four-photon entangled Dicke state with high fidelity.
abstract: We present the experimental observation of the symmetric four-photon entangled Dicke state with two excitations |D_{4};{(2)}. A simple experimental setup allowed quantum state tomography yielding a fidelity as high as 0.844+/-0.008. We study the entanglement persistency of the state using novel witness operators and focus on the demonstration of a remarkable property: depending on the orientation of a measurement on one photon, the remaining three photons are projected into both inequivalent classes of genuine tripartite entanglement, the Greenberger-Horne-Zeilinger and W class. Furthermore, we discuss possible applications of |D_{4};{(2)} in quantum communication.
authors.affiliation: Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Kiesel
authors.forename: C
authors.initials: C
authors.lastname: Schmid
authors.forename: G
authors.initials: G
authors.lastname: Tóth
authors.forename: E
authors.initials: E
authors.lastname: Solano
authors.forename: H
authors.initials: H
authors.lastname: Weinfurter