Quantum Secure Direct Communication with Five-Qubit Entangled State

Recently, a genuine five-qubit entangled state has been achieved by Brown et al. J. Phys. A 38 (2005) 1119. Later it was indicated that this state can be used for quantum teleportation and quantum state sharing. Here we build a quantum secure direct communication protocol with this state, and prove that it is secure in ideal conditions. In the protocol, the sender performs unitary transformations to encode a secret message on his/her particles and sends them to the receiver. The receiver then performs projective determinate measurement to decode the secret message directly. Furthermore, this protocol utilizes superdense coding to achieve a high intrinsic efficiency and source capacity.