Abstract: An experimental system of quantum communication that operated for free space is presented. This system is composed of two subsystems, which use attenuated laser or entangled photon pairs as the photon source, respectively. It can be used for experimental investigation in atmospheric characteristics of the system using a single photon source or entangled photon pairs, respectively, along with a comparison of characteristics between the two systems. The results show that the atmosphere in the lower layer plays an important role in affecting the quantum communication, and that the efficiency of the quantum key distribution is higher in the system using a single photon source.

Key words: quantum communication, communication experimental system, atmospheric effect, quantum simulation