Quantum Internet, two cities connected 500 kilometers apart

A “secure quantum link” has just been established between two Chinese cities more than 500 kilometers apart, with no need for intermediate encryption. Closer the development of a quantum internet network

(Image: Joshua Sortino/Unsplash)

A new step in the development of the network quantum internet 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 one secure quantum connection between two Chinese cities 511 kilometers apart without the need for an encrypted intermediary in between. The details were published in the magazine Nature Photonics.

The key concept of the development of a quantum internet network lies in the phenomenon ofentanglement, O quantum correlation, according to which two or more (quantum) particles are intrinsically linked together in such a way that each measurement operation carried out on one of them is instantly reflected on the other, or on the others. Let’s imagine, for example, that we have two quantistically correlated photons: by measuring the state of one of them, it is possible to deduce (and modify) the state of the other too, regardless of the distance that separates them. This mechanism, among other things, underlies the quantum cryptography: the particles entangled they can be used to create secret keys with which to decode the information, with the certainty that any undue attempt to access or tamper with sensitive data would lead to their irreparable destruction.

Already in previous studies, scientists had shown how it was possible to create a pair of photons entangled and transmit one of the two to a receiver, effectively creating a link based on a quantum key. In today’s experiment, the team of Qiang Zhang, of the University of Science and Technology of China, has extended the maximum distance of such a link by using a cable and an intermediate point that does not read the data, but only checks its integrity at the time it was sent. It works like this: at the ends of a fiber optic cable there are lasers, which send two beams of photons against each other. When two photons of the two beams are in phase (i.e., 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 and the signals coincide and these exchange the quantum key: in this way thehub central does not know the content of the message, but only if and when the two signals correspond.

An experiment recently conducted in Cambridge, UK, had already succeeded in showing the functioning of this system over a distance greater than 600 km, but in that case it had all 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 point out: “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 exceed the thousand kilometers. Who knows who will succeed first.

Categories:   Science