Sending signals through optical fiber - a reliable and rapid means of communication, but because of internal absorption and other effects, some of the photons is lost in a way that it becomes more critical, the smaller the total number of transmitted photons. This problem is particularly acute in quantum networks that involve a small number of photons entangled. In this case, transmission through the open space (vacuum or air) can lose less photons, but the method of transmitting data, the challenge is to fine-tune the transmitter and receiver at each other, the photons come exactly to the destination.
Group of China made a significant step towards solving this problem by developing a high-precision pointing and tracking. With this method, Huang Ying and colleagues, has made a quantum teleportation (copying the quantum state), with the help of many photons through the open space between the two stations at a distance of 97 km from each other, the two banks of the lake. In addition, they demonstrated entanglement two receivers at a distance of 101.8 km
Although the authors do not mention this in his article, their method of transmission, at the moment, is only possible at night. Nevertheless, they managed to reach a record distance for multi-photon entanglement teleportation and a three-point, and the tracking system can be used to make a reality of quantum communication with the satellite ground, at least at night.
Even a slight shift of the receiver due to atmospheric disturbances or tectonic activity, causes the laser sends a signal misses its target. This explains the need for a system of tracking (the settings on the target) in real time. The researchers solved this problem by using signal lasers that do not convey information in their bright signals, but can be used to set each other the receiver and transmitter.
This experiment was not only to confirm the viability of quantum communication through the open space, but also served as a practical proof of the efficiency of the quantum theory to the more remote distances.