Theory of the three-photon entangled state

Evaluation of the Greenberger-Horne-Zeilinger (GHZ) theory requires an entangled $n$-particle state with $n>~3$. To date, experimental achievement of a suitable GHZ state has proved elusive. This paper presents an approach to generate a three-photon entangled state and presents the theory of its space-time structure. Since an accurate picture of the space-time structure is important in understanding the two-photon state, an accurate picture of the three-photon state should be equally important.