Estratégias para a realizacão do protocolo de codificacão superdensa via canais quânticos puros e parcialmente emaranhados.

Abstract

The superdense coding protocol via partially entangled pure quantum channels is studied in the context of optimal discrimination among nonorthogonal states. Discrimination strategies with minimum error (ME), maximum condense (MC) and strategies that interpolate themwill be used to perform the protocol. First, it is shown that the superdence coding with null failure probability and maximum mutual information between the communicating parts is related to the ME strategy. Then, admitting a nonzero failure probability in the process, it is shown that the MC strategy enables the protocol to be performed with the maximumachievable mutual information for the channel with greater chance of success, which is higher than the deterministic case and depends only on the Schmidt rank of the entangled state. Furthermore, it is considered the iteration of the MC strategy in the case of failure and it is shown that there are channels for which it is possible to increase the success probability of performing the protocol with higher mutual information than the deterministic case. Lastly, it is analyzed the application of intermediate strategies between ME and CM in which it is shown to be possible to execute superdense coding with higher probability of success than allowed by the CM strategy and greater mutual information than provided by EM strategy. Analytical expressions for the mutual information are derived for all the studied protocols.