China successfully launched the world's first quantum satellite from the Jiuquan Satellite Launch Center in northwestern Gobi Desert at 1:40 am on Tuesday. [Photo/Xinhua]

Going global?

With the launch of QUESS, Chinese scientists now are having their eyes on a ground-to-satellite quantum communication system, which will enable global scale quantum communications.

In past experiments, quantum communications could only be achieved in a short range, as quantum information, in principle, could travel no more than 500 kilometers through optical fibers on the land due to the loss of photons in transmission, Pan explained.

Since photons carrying information barely get scattered or absorbed when travelling through space and Earth's atmosphere, said Pan, transmitting photons between the satellite and ground stations will greatly broaden quantum communications'reach.

However, in quantum communications, an accurate transmission of photons between the "server" and the "receiver" is never easy to make, as the optic axis of the satellite must point precisely toward those of the telescopes in ground stations, said Zhu Zhencai, QUESS chief designer.

It requires an alignment system of the quantum satellite that is 10 times as accurate as that of an ordinary one and the detector on the ground can only catch one in every one million entangled photons fired, the scientist added.

What makes it much harder is that, at a speed of eight kilometers per second, the satellite flying over the earth could be continuously tracked by the ground station for merely a few minutes, scientists say.

"It will be like tossing a coin from a plane at 100,000 meters above the sea level exactly into the slot of a rotating piggy bank," said Wang Jianyu, QUESS project's chief commander.

Given the high sensitivity of QUESS, people could observe a match being lit on the moon from the Earth, Wang added.

After years of experimenting, Chinese scientists developed the world' s first-ever quantum satellite without any available reference to previous projects. Now they are waiting to see QUESS's performance in operation.

According to Pan, his team has planned to initiate new projects involving research on quantum control and light transmission in space station, as well as tests on quantum communications between satellites, all-time quantum communications and the application of quantum key network.

"If China is going to send more quantum communication satellites into orbit, we can expect a global network of quantum communications to be set up around 2030," said Pan.