Quantum repeaters gave memory from diamonds

American physicists have created a quantum repeater based on diamond spins in the resonator and demonstrated it with a procedure of a quantum cryptographic key distribution. Using such repeaters, you can build a large quantum network, based on which we implemented a quantum Internet. Work published in Nature.

Quantum computers pose a potential threat to the whole of modern cryptography, but quantum cryptography — the technology of distribution of the cryptographic keys that are encoded in quantum States — is able to protect data from even the most powerful computers. The protocols of quantum cryptography is often implemented using photons propagating along the optical fiber, but, unfortunately, single photons are not ready to “live” in the optical fiber, so the distance between nodes of quantum networks still do not exceed hundreds of kilometres.

One possible solution is to install repeaters, which amplify the signal, and do not allow photons to fade. However, if the repeater is a classic, the whole is encoded in the quantum state information to become a classic and can be easily stolen. Therefore, scientists are working on quantum repeaters, which is an extremely difficult task.

A group of physicists from Harvard University and mit under the leadership of Professor Mikhail Lukin, co-founder of then quantum center, for the first time realized a quantum system that can serve as a repeater in quantum key distribution and, further, when transferring data via quantum Internet.

As an example, the group considered the Protocol of quantum key distribution between two users (Alice and Bob) with the use of a third party, which as a result does not receive the key, but provides two legitimate user important information about the quantum state used to distribute the key. This third party holds the bell States measurement conditions that initially sent Alice and Bob, and declares for open channel result. This result, together with information about the initial state, which is only Alice and Bob, gives a bit string that can be used as the key.

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