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A "secure quantum link" has just been established between two Chinese cities more than 500 kilometers apart, with no need for intermediate encryption. The development of a quantum internet network is closer

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A new step in the development of the quantum internet network of the future. The one that, at least in theory, should guarantee us ultra-secure communications, very fast connections, even more precise time synchronizations: a real revolution, which promises to radically change the way we exchange information. Today's news is that a team of Chinese scientists has managed to establish a secure quantum connection between two Chinese cities 511 kilometers apart without the need for an encrypted intermediary in between. Details were published in the journal Nature Photonics.

The key concept of the development of a quantum internet network lies in the phenomenon of entanglement, or quantum correlation, according to which two or more (quantum) particles are intrinsically linked together in such a way that each measurement operation that occurs on one of them is instantly reflected on the other, or on the others. For example, imagine having two quantum-correlated photons: by measuring the state of one of them, it is possible to deduce (and modify) the state of the other, regardless of the distance that separates them. This mechanism, among other things, is the basis of quantum cryptography: entangled particles can be used to create secret keys with which to decode information, with the certainty that any undue attempt to access or tamper with sensitive data would lead to the irreparable destruction of same.

Already in previous studies, scientists had shown how it was possible to create a pair of entangled photons and transmit one of them to a receiver, effectively creating a link based on a quantum key. In today's experiment, Qiang Zhang's team from the University of Science and Technology of China extended the maximum distance of such a link using a cable and an intermediate point that does not read the data, but only controls it. integrity with respect to the time they were sent. It works like this: lasers are placed at the ends of an optical fiber cable, which send two beams of photons against each other. When two photons of the two beams are in phase (ie, simplifying, when the peaks of the relative light waves are aligned) and meet at the intermediate point, this "warns" both the sender and the receiver that the signals coincide and they exchange the quantum key: in this way the central hub does not know the content of the message, but only if and when the two signals match.

An experiment recently conducted in Cambridge, UK, had already managed to show the operation of this system over a distance greater than 600 km, but in that case everything had happened in the laboratory; this time, however, the connection took place at 511 km real, between the cities of Jinan and Qingdao, as the authors of the work proudly underline: "In the laboratory you have a controlled environment, with an air conditioner that keeps the temperature stable . In the real world it is more difficult, since the phase of the photons can change as the temperature changes ”. Now the aim is to overcome the thousand kilometers. Who knows who will succeed first.


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