Generation and application of tripartite entangled state for continuous electromagnetic field

Experimental demonstration of quantum entanglement among more than two quantum systems with continuous spectra is summarized in the paper. The tripartite entangled state, named also GHZ-like state, is produced by distributing a two-mode squeezed state light to three parties using beamsplitter. A nondegenerate optical parameter amplifier (NOPA) operating at deamplification serves as the initial bipartite entanglement source. The output optical modes from the NOPA are a pair of bright EPR entangled beams with orthogonal polarizations, anticorrelated amplitude quadratures and correlated phase quadratures. The results confirm the existence of the quantum correlation among three amplitude quadratures of modes.