Observation of bipartite correlations using coherent light for optical communication

Bipartite polarization correlations of two distant observers are observed by using coherent noise interferences. This is accomplished by mixing a vertically polarized coherent light field with a horizontally polarized coherent noise field in a 50/50 beam splitter. The superposed light fields at each output port of the beam splitter are sent to two observers and then manipulated by using a quarter-wave plate and an analyzer. The bipartite correlations between the projection angles of two distant observers are established by analyzing their data through multiplication without any postselection technique. The scheme can be used to implement entanglement-based quantum cryptography in the future.