Kenichiro Furuta

ANALYZING THE EFFECTIVENESS OF THE QUANTUM REPEATER

The range of quantum key distribution is limited by exponential attenuation of photons in optical fibers. It is believed that a quantum repeater can improve the order of the attenuation and can be useful for extending the communication distance of QKD. It is already shown that quantum repeater is effective when not considering the repeater noise. In this paper, we analyze the effectiveness of the quantum repeater when considering the repeater noise. We point out that there is some threshold of length of EPR pairs, under which quantum repeater protocol is valid and over which quantum repeater is not valid. Besides, this threshold depends on the largeness of the repeater noise. So, it is important to suppress the repeater noise in order that the quantum repeater scheme can really improve the bit rate. We also analyze the effectiveness from the viewpoint of the security and show that QKD is secure even if quantum repeater is used.