The speed of light is not the limit for transmitting information - under some conditions, data can be transmitted twice as fast, scientists say in an article published in the journal Physical Review Letters.
“We were able to theoretically and experimentally show that quantum superposition allows one to exchange information in two directions at once, transferring only one particle, which was considered impossible from the point of view of classical physics. This allows you to create absolutely secure communication lines, in which not only data will be protected, but also the very direction of their transmission,”write Philip Walter and his colleagues from the University of Vienna (Austria).
According to the theory of relativity, nothing in the universe can move faster than the speed of light, since it takes an infinite amount of energy to overcome it. The same applies to information carriers - none of them can outrun light and instantly transmit data over great distances.
After the discovery of quantum teleportation and the phenomenon of entanglement of particles, a dispute arose about whether it is possible to transmit information faster than the speed of light in this way, and if so, how then to extract it. Most scientists believe that this is impossible, since teleportation data must be transmitted in a classical way. However, the state of the particles really changes instantly, regardless of the distance separating them.
Walter and his colleagues found that the speed limit of light can still be violated: they made information travel twice as fast, and this was allowed by the unusual properties of photons entangled at the quantum level. As the scientists explain, all this does not mean that the particle moves at twice the speed of light or that it carries two bits of data at once. The point is that the photon serves as a channel of not one-way, but two-way communication.
To do this, it is necessary to transfer the photon to such a quantum state that its position in space would be strongly "smeared" - that is, it would be simultaneously at different points on the path between the transmitter and receiver. Roughly speaking, each participant in the experiment will have a conditional half of the photon while it is in an indefinite state.
Thus, the subscriber of the quantum line can read the information that is transmitted to him and at the same time write his own. And his interlocutor will be able to read the data transmitted back, comparing what properties the photon possessed at the moment when the bit was written to it, and what they are now.
Such a trick, as the scientists note, does not contradict the theory of relativity, but allows data to be transmitted twice as fast as it is theoretically possible in accordance with the classical laws of physics.
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Guided by this idea, experimental physicists from the University of Vienna have built a quantum machine that allows such a two-way exchange of information in the real world using ordinary fiber optics, several lasers, light splitters and other optical devices.
The first experiments with this device showed that the transmitted data is automatically encrypted, so that hacking the communication line becomes a very difficult task. Moreover, if one of the subscribers transmits absolutely random data, the hacker, in principle, will not be able to extract it. This will make two-way quantum communication lines attractive to banks and government agencies.