Physicists have developed a 30-meter line quantum communication in the turbulent flow of water

Physics with the Protocol of the BB84 quantum communication has encrypted the message and gave a light beam under water with a turbulent over 30 meters. According to the obtained estimates of the maximum distance of the line of an encrypted connection can be up to 80 meters. Preprint published on the website

With the development of quantum computers and algorithms (e.g., Shor’s algorithm is able in logarithmic time — the processing time grows as the logarithm of a number is to decompose a large number into two simple multiplier to crack the key encryption algorithm RSA) is becoming increasingly important quantum algorithms encrypt the information. Since the implementation of the Protocol BB84 in 1984, quantum key distribution encryption has become the most reliable option for secure communication. To date, scientists have developed a commercially available device with quantum key distribution via optical fiber and new protocols to increase the security and refresh keys, and conducted experiments on the quantum transmission via a satellite communications channel.

Many protocols have the advantage due to multidimensional quantum States. Quantum information is usually encoded on one of the components of the degrees of freedom of a photon — polarization, delay, position and transverse moment. But you can use few degrees of freedom for the formation of more complex structures state of the photon, for example, the coherent combination of polarization and orbital angular momentum creates the state of a photon, which is used in microscopy, optical tweezers, classical and quantum communication. Read more about principles of quantum communication can be read in our article “Quantum alphabet: “Teleportation””.

Scientists implement the protocols of quantum key distribution through channels in free space, however, in recent years, researchers solve the problem of secure exchange of information between underwater research vehicles and vehicles on the surface of the water. Absorption of water waves of radio led to the dominance of acoustic technology in the exchange of information under water, but between 400 and 500 nanometers has a window of transparency, in which quantum and optical communications. Theoretical calculations showthat the maximum distribution of information in calm conditions — 300 meters at a wavelength of 418 nanometers, which is enough for research units. However, in the aquatic environment can not be ignored turbulent flow, which locally changes the refractive index of water and leads to a shift and distortion of the light beam. But because scientists are optimizing protocols to increase the distance and rate of key exchange.

Frederic Bouchard (Frederic Bouchard) with colleagues from the University of Ottawa explored the channel of underwater communication distance up to 30 meters in conditions of large losses of information. Scientists took into account the contribution of turbulence tested the BB84 Protocol with two variations: polarization and the two-dimensional structure of the photon.

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