What quantum projects Russian and foreign engineers are working on.
What are quantum networks
Quantum networks are data transmission systems, the principle of which is based on the laws of quantum mechanics. Information in such networks is transmitted through fiber optic cables with the help of polarized photons. One of the defining properties of photons is "fragility". They are destroyed by reading, so it is almost impossible to listen to quantum networks. Even if an intruder conducts a MITM-attack and connects to the data channel, the receiving party will immediately realize that the channel is compromised because it will receive "packets" with a lot of errors.
Quantum networks are used to distribute cryptographic keys between classic computer systems. For example, last year such a system was launched by Chinese engineers. It uses lasers to exchange data with satellites in orbit. A similar technology was proposed by German specialists in 2017 - they used the existing ground infrastructure and satellite hardware to transfer data.
Another application of quantum networks is the integration of quantum computers. Quantum machines already know how to solve some problems faster than classical computer systems - for example, in the field of machine learning and modeling. By combining quantum devices into clusters, physical and chemical simulations can be further accelerated (in particular, to contribute to the development of complex molecules for new drugs).
Who develops them
Many world institutions from America, Europe and Asia are involved in the development of quantum networks.
It is believed that the very first quantum network was developed in the U.S. by order of DARPA in the early 2000s. It is still functioning and connects several military laboratories in Massachusetts. Approximately at the same time quantum networks began to build and in Europe. At that time, the EU countries invested several million euros in the SECOQC project, within the framework of which they are designing quantum solutions to ensure national security.
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One of the main problems of quantum networks of that time is the impossibility to transmit the photon for a long distance (it rarely exceeded 50 km). Photons are "brittle" and easily destroyed by temperature (this is the so-called decoherence effect). Therefore, systems capable of increasing the transmission range are being actively developed today. For example, Dutch engineers create special repeaters that prolong the "lifetime" of quanta. Scientists are already laying the test network between Delft and The Hague. Presumably next year it will connect four cities in Europe at once. The same technology is being developed by specialists from Toronto, Osaka and Toyama universities. In February 2019, they presented the concept of a quantum repeater capable of transmitting photons at a distance of up to 800 km (in theory).
A team of physicists from the United States and Switzerland is working on the development in this field. At the end of last year, they introduced a very low noise photodetector that allowed the cryptographic key to be sent over a distance of 421 km, while maintaining a high data transfer rate. According to the developers, the network bandwidth is more than 100 times higher than in their previous experiments.
But the absolute record-breaker in range today is China. In 2016, Chinese engineers launched a quantum communication satellite and transmitted a cube over 1200 km away. Last summer, this satellite was used by engineers to make a secure call between the Chinese and Austrian academies of science.
How things are going in Russia
One of the first quantum networks in our country was deployed by engineers from ITMO in 2014. The fiber-optic cable was laid between two university buildings. Two years later, with the help of our colleagues from Kazan, the network became a multi-node one - four nodes were placed at a distance of 40 km from each other.
Three years ago, physicists from the Russian Quantum Center, the Russian Quantum Center, presented their quantum network. "Optika" was laid between two Moscow banks - the cable length was 30 km. And this summer physicists from RCC announced about creation of the first intercorporate quantum network in the Russian Federation. It connected the offices of Sberbank, Gazprombank and PwC, which offers consulting and auditing services.
Another example of the development was the presentation of a quantum telephone line by specialists from Moscow State University in 2017. Voice information between interlocutors was transmitted via a 50 km long fibre optic cable. Its encryption was the responsibility of the quantum key distribution server located 25 km away.
The number of quantum developments will continue to increase. And it will allow to create large quantum networks which will connect at once set of cities of the country.