A Continuous Variable Quantum Key Distribution Protocol Based on Entanglement Swapping of Quasi-Bell Entangled Coherent States

A continuous variable quantum key distribution protocol with entanglement swapping of quasi-Bell entangled coherent states is proposed. As the preliminary step, a sender shares quasi-Bell entangled coherent states with a receiver. After their measurements to distinguish the cases of a zero response, a nonzero even-photon response and an odd-photon response, two legitimate participants fulfill the task of key distribution. The correlations resulting from entanglement swapping of quasi-Bell entangled coherent states and the order rearrangement of transmitted states provide the possibility to protect secret key distribution. In the ideal channel, the success probability increases with the amplitude of the coherent state, and approaches unity when the amplitude of the coherent state is larger than two. However, in the loss channel, the decoherence will introduce error in the generated key, and the error rate increases with the amplitude of the coherent state. When the amplitude of the coherent state is smaller than 0.2 (or so), the error rate approaches zero, although the success probability is less than 0.5 in this case.