Physicists from MIPT found "forgotten" material, which can become the basis for high-speed quantum Internet. In an article published in the leading journal on quantum technologies Nature Partner Journal Quantum Information, it is shown how to increase to more than 1 Gb / s the speed of information transfer over a channel completely protected by the laws of physics, and make the quantum Internet as fast as the classical one.
The whole world is racing to create quantum computers. It has long been involved in industrial giants Google, IBM, Microsoft and the leading international research centers and universities. It is not known yet when such devices will appear, but the world is preparing for their appearance. The fact is that a quantum computer can cause a revolution in the field of information security. Confidentiality of transmitted information (personal correspondence, banking information, etc.), is provided today with encryption algorithms, for breaking into which a classical supercomputer will take years. It is expected that a quantum computer can do this in a fraction of a second.
Fortunately, an "antidote" has already been proposed that allows 100% protection of transmitted information from quantum computers and, in general, of all kinds of attacks. We are talking about quantum cryptography, the stability of which is ensured not by the complexity of deciphering, but by the laws of quantum physics. Its principle is based on the inability to create a copy of an unknown quantum state without changing the original. Therefore, the line of quantum communication can not be listened to unnoticed by the sender and the recipient. A quantum computer here does not help attackers - even if they intercept transmitted data, this is immediately known, and stealthily stealing information will not come out.
Transmit information best with the help of quanta of light - photons, - carrying quantum bits. It is extremely important to use single photons, otherwise the attacker will be able to intercept additional photons and receive a copy of the message. The principle of generating single photons is quite simple. An excited quantum system can go over to the ground state with the emission of exactly one quantum of light. It remains only to find a quantum system suitable for practical use. This is the whole complexity. For example, quantum dots work well only at very low temperatures (of the order of -200 ° C), and ultramodern two-dimensional materials, such as graphene, simply can not often emit photons under electric excitation.
The solution of the researchers from MIPT consists in using the material already forgotten in optoelectronics - silicon carbide. "In 2014, we almost accidentally drew attention to silicon carbide and immediately appreciated its potential, " says Dmitry Fedyanin , senior research fellow at the Laboratory of Nanooptics and Plasmonics. However, according to him, for the first time one-photon electroluminescence in this semiconductor was obtained in 2015 by a group of scientists from Australia.
Strangely enough, it was silicon carbide that started the modern optoelectronics: it was the first to observe electroluminescence (glow when electric current was passed), in the 1920s the first light-emitting diodes were demonstrated on its basis, and in the 1970s, They were produced in the USSR on an industrial scale. However, in the 1980s, silicon carbide was completely displaced from optoelectronics by direct-gap semiconductors and was almost forgotten, so today it is better known as a very hard and heat-resistant material from which electrical components, bulletproof vests and brake pads of Porsche, Lamborghini and Ferrari supercars are manufactured.
Dmitry Fedyanin and colleagues from the laboratory of nanooptics and plasmonicsThe center of photonics and two-dimensional materials of MIPT in their work investigated the physics of single-photon electroluminescence of color centers in silicon carbide and developed a theory that explains and accurately reproduces experimental results. Color centers are point defects of the crystal lattice, which have an optical transition in the spectral region where the defect-free crystal is transparent. They play a key role in single-photon electroluminescence. Using the developed theory, the researchers showed how to improve the carbide-silicon single-photon LED to increase the photon emission rate to several billion per second. This is what is required for the implementation of protocols of quantum cryptography at a speed of about 1 Gbit / s. Two other authors of the study, Igor Khramtsov and Andrei Vishnevy, pay attention to the fact that, most likely, in the future there will be other materials that will approach silicon carbide in terms of the brightness of single-photon radiation, but unlike silicon carbide, devices from them can not be manufactured industrially in the same technological process as most modern microcircuits. Thanks to compatibility withCMOS process, single-photon sources based on silicon carbide are practically unattainable for competing materials and can solve the problem of low-capacity quantum communication lines.
The study was supported by a grant from the Russian Science Foundation No. 17-79-20421.