Tripartite entanglement swapping of bright light beams

We propose a new and experimentally realizable continuous variable quantum communication protocol named tripartite entanglement swapping. Three optical modes, which are not in a tripartite entangled state initially, can be entangled by means of the direct detections of Bell-states, the amplitude and phase modulators, and the beamsplitters. The initial bipartite and tripartite entangled states are produced with the bright single mode quadrature squeezed state of light and linear optics. We analystically proved that tripartite entanglement swapping can be accomplished with two schemes in which a tripartite entangled state or two bipartite entangled states serve as quantum channel respectively. The direct detection of Bell-state is applied in the proposed schemes, thus the needs for local beams used in homodyne detectors and the trouble for mode matching are significantly avoided.