Quantum dense coding exploiting a bright Einstein-Podolsky-Rosen beam

A bright Einstein-Podolsky-Rosen (EPR) beam with autocorrelation of amplitude quadratures and correlation of phase quadratures was used to experimentally obtain a highly efficient quantum dense coding for continuous variables. Two bits of classical information were encoded on two quadratures of a half of a bright EPR beam. These bits were then simultaneously decoded by the other half of the EPR beam with sensitivities beyond that of the shot noise limit. Experiments showed a high degree of the immunity to unauthorized eavesdropping.