- Sergey Pavlovich, in your interviews with RT you have already talked about how quantum communication works. Remind me, please, in a nutshell - what is quantum communication, what features does it have?
- The main feature and advantage of quantum communication is an exceptional level of confidentiality.
In general, the secrecy of communication is usually ensured by frequently changing cryptographic keys that both subscribers have.
Quantum communication uses a new way of distributing cryptographic keys - quantum.
The keys are formed using a stream of single photons.
Any external influence will lead to the destruction of the state of the photon.
If the level of errors during key generation exceeds the critical one for the protocol used, the communication session is terminated.
The only measurement is made when the photon reaches the receiving device at the other end of the network, during which the particle disappears.
Quantum communication uses two data transmission channels: quantum states of light are transmitted via the quantum channel, and auxiliary information necessary for the correct operation of the quantum cryptography protocol is exchanged via the classical channel.
Moscow State University
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Quantum communication technology assumes that keys are first distributed between subscribers, and then the transmitted information is encrypted with them.
Information encrypted with quantum keys can be transmitted both via optical fiber and atmospheric (wireless) channels.
Quantum communication technology is actively developing both in Russia and around the world.
In our country, such a connection is already presented not just in the form of one line connecting two subscribers, but as full-fledged networks.
One of these networks was presented at the end of last year at Lomonosov Moscow State University.
This is an extensive system, which now includes more than 20 subscribers on the MSU campus, and is also extended to the office of our Center's industrial partner, InfoTeKS, a manufacturer of quantum equipment, which is located more than 40 kilometers from us.
- How is the quantum transmission of information via atmospheric communication channels arranged? How does this technology work?
— The technology works with the use of a laser — a source of quasi-single-photon states.
Another name for a laser is an optical quantum generator.
For quantum communication, the laser is tuned so that there are very few photons in each of its pulses.
Each photon is given certain characteristics depending on the quantum cryptography protocol used.
Not all photons reach the receiving device, but some reach the target.
On the receiving side there is a photon registration module - a lens with a sufficiently high aperture (aperture is a characteristic of an optical device that describes its ability to collect light. -
RT
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Next, the photon enters a special optical system, a detector, which converts the received data into pulses to form a cryptographic key.
The use of an atmospheric communication channel has both pluses and minuses.
Minus - for data transmission, it is necessary that the subscribers are in direct visibility, so that there are no obstacles between them.
Such a connection is highly dependent on the weather - during snowfall or fog, cryptographic keys cannot be distributed over the atmospheric channel.
But they have already learned how to deal with this problem - the keys are distributed with a small margin, old keys can encrypt new information for some time.
In our systems, keys (256 bits) are generated at a rate of a few pieces per minute or faster.
The advantage is that the wireless channel can be used where fiber optics cannot be laid.
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– The Center for Quantum Technologies of the Faculty of Physics of Moscow State University recently tested equipment for transmitting quantum keys and information protected by quantum keys via atmospheric communication channels. Please tell us more about this work.
— This work has been carried out by us for a very long time, we have already tested such equipment many times.
The day before, we just took another step forward within the framework of this project, reached a new technical level.
The system consists of two terminals that are connected to each other through an atmospheric channel at a distance of several kilometers, within sight.
Moreover, we have already made a system for distributing keys through the atmospheric channel and to a mobile object - it was an unmanned aerial vehicle that flew within a radius of several hundred meters around the transmitter.
We also have another project, which is currently stalled due to bureaucratic delays - the distribution of keys to low-orbit satellites.
In this area, our Center has a great start: the necessary equipment has been developed and mock-up samples have been manufactured.
— How sophisticated equipment is needed to implement quantum communication through an atmospheric channel?
- Both special equipment and classical equipment, which is used in telecommunications, are used.
Special equipment is used to generate photons, convert them and register them.
These are unique devices, although, I repeat, we and other scientific teams have been working in this area for a long time.
The usual telecommunications equipment is also used - telescopes, devices for converting optical signals and controlling them.
- What is the maximum distance you can transfer data in this way?
- This technology works best in space, where there are no aerosols and impurities.
There is such a thing as diffraction divergence.
Typically, this divergence has a small angle, so in space data can be transmitted thousands of kilometers in line of sight.
Record values in terrestrial conditions are hundreds of kilometers, but in a metropolis it is usually several kilometers due to high atmospheric pollution.
However, there are many customers for whom it is important to provide such a connection not even for kilometers, but for hundreds of meters.
This is necessary when, over a longer distance, quantum communication is already provided through an optical fiber, but there are small areas where it is difficult or impractical to conduct it.
It is in these areas that data transmission via the atmospheric channel is activated.
Figuratively, these sections can be called the "last mile".
As a rule, we are talking about the offices of large companies.
There are companies that are located in several buildings, then the atmospheric channel allows you to establish encrypted communication between them.
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- You have already mentioned interference in the form of aerosols, snow, which interfere with such communication. Are there any other solutions to this problem other than using the old keys?
- Such solutions do not exist, possible interference - payment for the secrecy of communication, overhead, figuratively speaking.
In what other areas can this technology be applied? For example, they write about its possible use for communication with unmanned vehicles.
- Yes, we have already developed such equipment that can work on unmanned vehicles - if necessary.
The degree of data protection in this case is very high, I do not think that unmanned vehicles need such a level of confidentiality.
The main application is still communication over short distances in urban areas, as well as, in the future, use in the space field.
For space, this technology is very relevant, because its use on low-orbit satellites will make it possible to cover very large areas with secure communications.
This is a difficult task, but it has already been practically solved.
Today in Russia this is no longer even a technical, but a purely organizational issue.