After more than two decades of development, quantum communication has now reached a rather advanced level. The development clearly points towards a future quantum internet. After reviewing some of the early experiments, particularly on quantum cryptography and on long-distance quantum teleportation, I will give a brief overview of the current state with focus on quantum communication with individual photons. Parallel to the communication experiments themselves there have been an increasing number of tests of quantum entanglement as signified by the Einstein-Podolsky-Rosen Paradox and Bell's Inequality. Such experiments, besides closing any possible loopholes for a local realist, i.e. classical, view of the world, also provide confirmation that unconditionally secure quantum cryptography is possible. The most recent experiments include long-distance quantum teleportation, including long-distance entanglement swapping, which is the teleportation of an entangled state. Such experiments are considered to be a basic ingredient of future quantum repeaters between quantum computers. Further, for most quantum communication experiments, a qubit, i.e. a two-state quantum system, is the basic carrier of information. In recent experiments, it has been shown that this limit can be broken by high-dimensional states, particularly multi-mode states, and by photon states which carry orbital angular momentum. Such techniques have also been tested over long distances in free space despite expectations that atmospheric fluctuations might make the communication impossible. Most recently, the Chinese quantum satellite Micius has established various quantum techniques for communication from ground to satellite or between ground stations. Of those, I will focus particularly on intercontinental quantum key distribution, as recently established. The long-term vision is a world-wide network combining quantum satellites and large-scale ground state fiber networks.
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