Quantum secure direct communication with χ-type entangled states

In this paper, a quantum secure direct communication protocol with chi-type entangled states parallel to chi(00)>(3214) is proposed. We analyze the security of this protocol and prove that it is secure in ideal conditions. Then, an alternative way is presented to ensure the security of this protocol in a noisy channel. Moreover, this protocol utilizes quantum superdense coding to achieve a high intrinsic efficiency and source capacity. The practical implementation of this protocol is also discussed.