A Three-stage Phase Encoding Technique for Quantum Key Distribution

The only known transmission technique that provides unconditional security is based on quantum cryptography. The current workhorse of quantum cryptography, more precisely, quantum key distribution (QKD), is based on the BB’84 protocol. Most commercial QKD implementations are based on phase-coding the BB’84 protocol, where the unbalanced Mach-Zehnder Interferometer (UMZI) is used as the information coder and decoder. This paper presents a three-stage phase encoding quantum key distribution protocol which is based only on one two-way quantum channel. This protocol does not need key sifting for key establishment. The proposed technique thus obviates the use of a classical communication channel for key sifting and key distillation which are subject to eavesdropping. The proposed technique thus increases the key efficiency and security compared with the current techniques.