ON THE USE OF DOUBLE ENTANGLEMENT IN 4-PHOTON EXPERIMENTS

Although the vast majority of Einstein-Podolsky-Rosen experiments have utilized states that are entangled with respect to only one type of o bservable, it is possible to have two-particle states that are simulta neously entangled in both spin and space-time variables. By performing certain measurements which exploit the double entanglement of two of these special states, a four-photon entangled state can be constructed for verifying the recent demonstration of nonlocality by Greenberger, Home, and Zeilinger.