Quantum Secure Direct Communication Scheme in the Non-symmetric Channel with High Efficiency and Security

By analyzing the basic properties of a class of three-particle W states, we show how to establish a non-symmetric channel to realize a quantum dense code scheme, each quantum pair can carry log₂ 18 bits of classical message by employing different kinds of unitary transformation in three-dimensional Hilbert space, which can improve the transmission efficiency of classical message. Based on this quantum dense code, we propose a novel quantum secure direct communication scheme. The security of the scheme is also discussed in detail, and the error rate for eavesdropper is 50 %.