Quantum secure direct communication with<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>χ</mml:mi></mml:math>-type entangled states

In this paper, a quantum secure direct communication protocol with $\ensuremath{\chi}$-type entangled states ${\ensuremath{\mid}{\ensuremath{\chi}}^{00}⟩}_{3214}$ 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.