Simplified quantum secure direct communication system with decoy states based on linear optical devices

A simplified entanglement-based quantum secured direct communication system over optical fibers is proposed. Instead of the complicated optical and electronic devices used in the transmitter of standard systems for security checks, a decoy-state generator is integrated with the encoder. This provides a simple yet efficient and easy to implement solution to reveal the presence of intruders. A significant advantage of the proposed system is that it eliminates the need for quantum memory elements in the security check procedure performed in the transmitter. This greatly enhances the information transmission capacity of the quantum channel. All system parameters are defined from commercial specifications to account for components’ non-idealities. A numerical simulation shows that, after a 10-km transmission distance, a quantum state visibility of the polarization entangled Bell state of 88.57% is found, and a maximum coincidence rate of 4  ×  107  Hz is achieved.