Quantum Cryptography Experiments in Orbit

I can’t pretend to really understand quantum cryptography (QC), but it is clearly coming fast. In case there were any doubt of the importance of this technology, a team of Chinese researchers reports this month on their ground breaking Micius satellite experiment, which has demonstrated um entanglement over a distance of 1200 KM [2].  Wow!

(It’s so cool that the technical paper gets to cite Einstein and Schrödinger from the 1930’s.  It’s almost worth doing the experiment, just for the chance to cite these foundational work!)

This quantum entanglement phenomenon offers a technique for very secure data transmission—it is the ultimate tamper proof channel. But it’s kind of slow and very expensive, so the first applications will be key distribution for secure cryptography. (For example, to distribute root keys for large networks.)

One of the difficult problems has been that in the atmosphere or even glass fiber, photons scatter so much that the phenomenon has a limited range (around 200 KM). Some systems have explored relaying through multiple short hops, though that requires securing all the relay units.

The Micius experiment attacks the problem by using an orbiting satellite. The downlinks only have to push through the height of the atmosphere (~10KM), the rest of the trip is in near vacuum. Thus, two ground stations are effectively able to link no matter how far apart they are on the surface.

The implications are obvious. If this technology can be developed, it will be possible to create very secure key distribution networks—though it will be very expensive, and not likely to be available for “open source” uses. There may also be other challenges, such as the potential vulnerability of orbiting satellite to attack. (It wouldn’t do to have your critical key distribution channel easy to shoot down.)

But these results represent a great technical achievement indeed! I’m not enough of an expert to really say, but I gather that there are a lot of fiddly details, not to mention extremely precise engineering to get right.

I have to say that it is remarkable how audacious the Chinese program is, and also how open they have been. Other nations are surely at work on these problems, there has been nothing so public as China’s remarkable efforts.

Well done, all!


  1. Roland Pease, China’s quantum satellite in big leap, in BBC News: Science & Environment. 2017. http://www.bbc.com/news/science-environment-40294795
  2. Juan Yin, Yuan Cao, Yu-Huai Li, Sheng-Kai Liao, Liang Zhang, Ji-Gang Ren, Wen-Qi Cai, Wei-Yue Liu, Bo Li, Hui Dai, Guang-Bing Li, Qi-Ming Lu, Yun-Hong Gong, Yu Xu, Shuang-Lin Li, Feng-Zhi Li, Ya-Yun Yin, Zi-Qing Jiang, Ming Li, Jian-Jun Jia, Ge Ren, Dong He, Yi-Lin Zhou, Xiao-Xiang Zhang, Na Wang, Xiang Chang, Zhen-Cai Zhu, Nai-Le Liu, Yu-Ao Chen, Chao-Yang Lu, Rong Shu, Cheng-Zhi Peng, Jian-Yu Wang, and Jian-Wei Pan, Satellite-based entanglement distribution over 1200 kilometers. Science, 356 (6343):1140, 2017. http://science.sciencemag.org/content/356/6343/1140.abstract

 

Space Satruday

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