Saturday, January 12, 2019

China - Communications in Space

The following article is quoting Chinese publications on cutting-edge laser communications in space and which makes up for one of China's most ambitious national programs. Due to the complex character of that subject, I tried to keep myself as close as possible to the original text in order to avoid misinterpretation. Only slight editorial changes have been made to the quotations.

On January 9 in 2015, the first prize of the National Technology Invention Award, and which represents the highest level of invention and creation in China, was awarded to Prof. Ma Jing and his research team at the Harbin Institute of Technology by China's prime minister Li Keqiang.

"Prof. Ma Jing and Prof. Tan Liying successfully carried out the 'Star-Earth Laser-Link-Communications Test' which is an important milestone in the history of China's satellite communications technology development, marking China's space high-speed information transmission, a high-tech aerospace cutting- edge field."

Harbin Institute of Technology - Prof. Ma Jing (l) and Prof. Tan Liying (r)


More accurate, however, is a Chinese publication in the US magazine Science, and which was launched on June 16, 2017. That publication deals with "Satellite-based entanglement distribution over 1200 kilometers". In other words it's about "Space calling Earth, on the quantum line". All of the authors belong to research facilities located in China.

"Any successful quantum communications network will rely on the ability to distribute entangled photons over large distances between receiver stations. Up to then, earthbound free-space demonstrations had been limited to line-of-sight links across cities or between mountaintops. Scattering and coherence decay have limited the link separations to around 100 km. Yin et al. now used the Chinese Micius satellite, which was launched last year and is equipped with a specialized quantum optical payload. They successfully demonstrated the satellite-based entanglement distribution to (terrestic) receiver stations separated by more than 1200 km. The results obtained are illustrating the possibility of a future global quantum communications network."

The signal attenuation of measured photon activity as a
function of varying length of the communications path.

"Quantum entanglement, first recognized by (Albert) Einstein, Podolsky, and Roson, as well as Schrödinger, is a physical phenomenon in which the quantum states of a many-particle system cannot be factorized into a product of single-particle wave functions, even when the particles are separated by large distances. Entangled states have been produced in laboratories and exploited to test the contradiction between classical local hidden variable theory and quantum mechanics by using Bell’s inequality. It is of fundamental interest to distribute entangled particles over increasingly large distances and study the behavior of entanglement under extreme conditions."

In the space module, photons of different quantum status were generated by a pump laser
(PL) and subsequent polarizing crystal (PBS) that is splitting the laser beam into differently
polarized photons. An integrated system of mirrors is comprising fixed dichromatic mirrors
DM1/DM2 and piezo-electrically steered mirrors PI for fine adjustment. It is used to aligne
both kinds of photons before their emission. Quarter-wave and half-wave plates QWP/HWP
are included.

"Practically, large-scale dissemination of entanglement — eventually at a global scale — is useful as the essential physical resource for quantum information protocols such as quantum cryptography, quantum teleportation, and quantum networks."

[Science - American Association for the Advancement of Science 16 June 2017]

There have been considerations, published by other sources, to use photon-entanglement in the creation of secure communication lines that could not be hacked. Any unauthorized interference with such line would lead to a quantum switch of entangled photons and such trigger off the alarm at the connected receiving station.

Up to now, we don't know for sure whether photon-entanglement is playing a role in China's brandnew communications line named the "Magpie Bridge", and which already enables data transfer between Earth and the backside of the Moon. However, it would be a contradiction to enormous Chinese efforts in this field, if such option was not included in the plannings of the Magpie project.

China's relay satellite system "Magpie Bridge". [搜狐2019年01月02日]

Related Subjects:

Here's another future application of quantum mechanics and quantum state entanglement.
According to IBM Q, 1st US manufacturer of quantum computers, some systems are already
available and are allegedly working under stable conditions, i.e. without any mechanical or
thermal disturbances from the outside. IBM Q's brandnew commercial video was launched
on January 8, 2019:

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