  Quantum entanglement swapping is one of the most promising ways to realize
the quantum connection among local quantum nodes. In this Letter, we present an
experimental demonstration of the entanglement swapping between two independent
multipartite entangled states, each of which involves a tripartite
Greenberger-Horne-Zeilinger (GHZ) entangled state of an optical field. The
entanglement swapping is implemented deterministically by means of a joint
measurement on two optical modes coming from the two multipartite entangled
states respectively and the classical feedforward of the measurement results.
After entanglement swapping the two independent multipartite entangled states
are merged into a large entangled state in which all unmeasured quantum modes
are entangled. The entanglement swapping between a tripartite GHZ state and an
Einstein-Podolsky-Rosen entangled state is also demonstrated and the dependence
of the resultant entanglement on transmission loss is investigated. The
presented experiment provides a feasible technical reference for constructing
more complicated quantum networks.
