Quantum networks: what they develop in Russia and abroad

    In the past, we talked about the prospects for quantum networks and the complexities that confront their developers. Today we’ll tell you about which projects domestic and foreign researchers are working on. If you are interested in this topic, we invite under the cat.

    / Flickr / Groman123 / CC BY-SA

    Where and why are quantum networks needed

    Data exchange in quantum networks takes place with the help of polarized photons, called qubits. Such networks cannot be “listened to”, since qubits are very fragile and change their meaning when read. As a result, parties exchanging data over secure channels can immediately identify the MITM attack. In this case, the phenomenon of quantum entanglement allows you to learn about the change in the properties of quantum particles at a distance. This feature can be used to generate random numbers at two points simultaneously.

    For these reasons, quantum networks have found application in distribution systems and the generation of cryptographic keys.

    Foreign developments

    The development of quantum cryptographic key distribution systems is being carried out by many European countries, as well as the USA, China and other countries.

    The first working draft of the quantum network was developed by DARPA (United States Department of Defense Office) back in 2001. It was created by the same organizations that previously engaged in the implementation of ARPNET. Now the quantum network is deployed in Massachusetts, where it connects several scientific and military organizations.

    Some time later, the first commercial solutions appeared in the field of quantum cryptography. In 2002, Navajo debuted from MagiQ Technologies , which is used by NASA. The system uses the BB84 quantum key distribution protocol . This protocol assumes that the communication nodes have two connections: fiber-optic (quantum), over which the exchange of cryptographic keys, and the classic Internet connection for data transfer. This approach is used today.

    At the very beginning of zero, European researchers also carried out work on quantum cryptography technologies. An example would be the SECOQC project ., created to maintain the state security of the European Union. In 2004, the EU invested € 11 million in the project, and in 2008 the network was launched in Vienna.

    At that time, the main problem faced by the researchers was the difficulty of transmitting entangled qubits over long distances. In particular, the length of the MagiQ quantum network was limited to 30 kilometers.

    The impact of the external environment destroys quanta (the effect is called decoherence ). This effect is also the reason for the complexity of the long retention of the "entangled" state of quantum particles.

    Today, there are active developments that address this difficulty. In particular, employees of the Delft Institute in the Netherlands are working on repeaters that should help increase the scale of networks. To conduct tests, they build a ten-kilometer quantum network between the city of Delft and the Hague. Later - by 2020 - it should connect four European cities.

    Also, some countries are working on the implementation of satellite quantum cryptographic key distribution systems. For example, last year, Chinese engineers made the first ever quantum teleportation in the transmission of data from space .

    The photons were transmitted to the ground using lasers. To reduce the influence of decoherence on the transmitted quantum particles, the satellite was put into a 500-kilometer orbit. Thus, the particles of light overcome a significant part of the path in a vacuum. At the same time, the influence of the atmosphere was reduced by locating the receiving station at a height of four kilometers above sea level in Tibet. At the beginning of this year, the staff of the Beijing Academy of Sciences used a satellite to hold a teleconference using quantum communication.

    / Flickr / Jeremy Atkinson / CC BY

    How are you doing in Russia?

    Experiments with quantum networks and the distribution of quantum keys are conducted in Russia. It is believed that the first in our country quantum network (and, more precisely, the line) was laid by researchers from ITMO University between the two buildings of the university.

    A couple of years later, the same specialists, together with colleagues from the Kazan Quantum Center, launched the first multisite quantum network in the Russian Federation . In total there were four nodes, they were located at a distance of 40 km from each other. Now researchers are working on laying a network from Kazan to Naberezhnye Chelny and are negotiating with financial organizations interested in adapting the technology to implement encrypted communications.

    Another development example - in 2016, physicists from the Russian Quantum Center (RCC) laid the first quantum network in the conditions of the city. Fiber optic cables stretched between two bank branches in Moscow, located 30 kilometers from each other. Now experts from the RCC are working on a 250-kilometer line of quantum communication. It will run between the RCC office, the Skolkovo technology park and the Sberbank data center. The network is divided into ten sections with a length of 80 kilometers. Some segments of the network plan to transmit data using IR lasers.

    It can be expected that projects now sponsored by financial, scientific, and government institutions will, over time, allow for the organization of larger quantum networks.

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