Controlled Quantum Secure Direct Communication Protocol Based on Three-Particle W State Decoy

Three-particle W state decoy is introduced in controlled quantum secure direct communication to improve the eavesdropping detection probability and prevent the double-CNOT attack. Each particle of three-particle W state decoy is inserted into sending particles to detect eavesdroppers. The decoy particles inserted randomly can prevent the receiver from obtaining the correct correlation between particle 1 and particle 2 before sender coding on them, so that he can not get any secret information without controller's permission. In the security analysis, the maximum amount of information in a qubit is obtained by introducing the entropy theory method, and two decoy strategies are compared quantitatively. If eavesdroppers intend to eavesdrop on secret information, the per qubit detection rate can reach 64% by using three-particle W state as decoy, but 58% by using extended three-particle GHZ state as decoy.