期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：48
页码：13648-13653
DOI：10.1073/pnas.1612023113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceLight is the main carrier of information. Its spatial mode allows the encoding of more than 1 bit per photon, and thus can increase the information capacity. For communication purposes, these modes need to be transmitted over large distances. Nowadays, fiber-based solutions are in their infancy, which renders free-space transmission the only possibility. We present an experiment where we investigate the behavior of the spatial modes after a distance of 143 km. With the help of an artificial neural network, we distinguished different mode superpositions up to the third order with more than 80% accuracy. Our results indicate that with state-of-the-art adaptive optics systems, both classical communication and entanglement transmission is feasible over distances of more than 100 km. Spatial modes of light can potentially carry a vast amount of information, making them promising candidates for both classical and quantum communication. However, the distribution of such modes over large distances remains difficult. Intermodal coupling complicates their use with common fibers, whereas free-space transmission is thought to be strongly influenced by atmospheric turbulence. Here, we show the transmission of orbital angular momentum modes of light over a distance of 143 km between two Canary Islands, which is 50x greater than the maximum distance achieved previously. As a demonstration of the transmission quality, we use superpositions of these modes to encode a short message. At the receiver, an artificial neural network is used for distinguishing between the different twisted light superpositions. The algorithm is able to identify different mode superpositions with an accuracy of more than 80% up to the third mode order and decode the transmitted message with an error rate of 8.33%. Using our data, we estimate that the distribution of orbital angular momentum entanglement over more than 100 km of free space is feasible. Moreover, the quality of our free-space link can be further improved by the use of state-of-the-art adaptive optics systems.
关键词：high-dimensional states ; long-distance communication ; orbital angular momentum ; atmospheric turbulence
