New progress on experimental quantum cryptography——experimental free-space distribution of entangled photon pairs over 13km

We have experimentally realised free\|space distribution of entangled photon pairs through a noisy ground atmosphere of 13km. It is shown that the desired entanglement can still survive after both photons have traversed a distance beyond the effective thickness of the aerosphere. We observe a spacelike separated violation of the Bell\|Clauser\|Horne\|Shimony inequality of 2.45±0.09. With this source we have demonstrated the BB84\|Ekert91 quantum cryptography protocol. Our experiment has shown for the first time the feasibility of using entangled photons for ground\|to\|satellite quantum communication, and presents a significant step towards satellite\|based global quantum communication in the future. We first review the rapid progress in quantum cryptography over recent years and then describe our experiment in detail.