Quantum Cryptography Using the International Space Station

With present technology, long-distance quantum communication demands the use of satellites. This is because quantum signals cannot be amplified and quantum repeaters do not exist yet. With space quantum communication, one could connect any two locations on earth by quantum cryptography. This can be done by using a single down-link for each location separately. A joint quantum key is then obtained by XOR-operations on the trusted satellite. Alternatively, one could employ two downlinks, at the same time sending two entangled photons to two different ground stations. This clearly limits the range. From a practical point of view, the link attenuations expected for satellite links are of the same order of magnitude as the link budgets in present long-distance quantum communication experiments between the Canary Islands of La Palma and Tenerife. These experiments therefore confirm the feasibility of space quantum communication. In the talk, some of these experiments will also be reviewed and their implications for space links will be discussed.