Probabilistic Superdense Coding Based on the Mixed Entangled State

Ideal dense coding protocols allow one to use prior maximal entanglement to send two bits of classical information by the physical transfer of a single encoded qubit. We investigate the case when the prior entanglement is not maximal and the initial state of the entangled pair of qubits being used for the dense coding is a mixed state. The upper bound on the probability to do dense coding is analyzed, and then the capability of dense coding is investigated in this paper.