We report a free-space entanglement-based quantum key distribution experiment, implementing the biased basis protocol between two sites which are 15.3 km apart. Photon pairs from a polarization-entangled source are distributed through two 7.8-km free-space optical links. An optimal bias 20:80 between the X and Z basis is used. A post-processing scheme with finite-key analysis is applied to extract the final secure key. After three-hour continuous operation at night, a 4293-bit secure key is obtained, with a final key rate of 0.124 bit per raw key bit which increases the final key rate by 14.8% comparing to the standard BB84 case. Our results experimentally demonstrate that the efficient BB84 protocol, which increases key generation efficiency by biasing Alice and Bob's basis choices, is potentially useful for the ground-satellite quantum communication.
@article{arxiv.1304.6462,
title = {Entanglement-based quantum key distribution with biased basis choice via free space},
author = {Yuan Cao and Hao Liang and Juan Yin and Hai-Lin Yong and Fei Zhou and Yu-Ping Wu and Ji-Gang Ren and Yu-Huai Li and Ge-Sheng Pan and Tao Yang and Xiongfeng Ma and Cheng-Zhi Peng and Jian-Wei Pan},
journal= {arXiv preprint arXiv:1304.6462},
year = {2015}
}