Experimental Observation of Four-Photon Entangled Dicke State with High Fidelity

Nikolai Kiesel, Christian Schmid, Geza Toth, Enrique Solano, Harald Weinfurter

Published 2006-06-28Version 1

We present the experimental observation of the symmetric four-photon entangled Dicke state with two excitations $|D_{4}^{(2)}>$. A simple experimental set-up allowed quantum state tomography yielding a fidelity as high as $0.844 \pm 0.008$. 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 GHZ and W class. Furthermore, we discuss possible applications of $|D_{4}^{(2)}>$ in quantum communication.