China to launch first space-based quantum communications experiment
Baku, June 12 (AZERTAC). he "Chinese Quantum Science Satellite" will launch in 2016 and aim to make China the first space-faring nation with quantum communication capability.
The ability to send perfectly secure messages from one location on the planet to another has obvious and immediate appeal to governments, the military and various commercial organizations such as banks. This capability is already possible over short distances thanks to the magic of quantum cryptography, which guarantees the security of messages — at least in theory.
For the moment, however, quantum cryptography works only over distances of 100 km or so. That's how far it is possible to send the single photons that carry quantum messages through an optical fiber or through the atmosphere.
Last year, we watched as European and Chinese physicists battled to claim the distance record for this technology with the Europeans finally triumphing by setting up a quantum channel over 143 kilometers through the atmosphere.
That distance is a good fraction of the way into space. And the reason that's important is that it's a stepping stone to sending quantum messages to orbiting satellites which can then route the messages to almost anywhere else on the planet.
Today, the Chinese claim another small victory in this quantum space race. Jian-Wei Pan at the University of Science and Technology of China in Shanghai and his fellow researchers say they've bounced single photons off an orbiting satellite and detected them back on Earth. That's significant because it simulates a satellite sending single photons from orbit to the surface, crossing off another proof-of-principle milestone in their quantum checklist.
The experiment is simple in principle. These guys have two telescopes in a binocular formation which they pointed at a satellite orbiting at an altitude of 400 kilometers. This satellite is covered with reflectors capable of bouncing a laser beam from Earth back to its original location.
They used one of the telescopes to send pulses of light towards the satellite and the other, with a diameter of 60 cm, to look for the reflection.
Of course, the Earth's atmosphere absorbs a very high percentage of the photons transmitted from the ground. So Pan and his team produced each pulse with just enough photons so that, on average, just one would reach the satellite and be reflected back to Earth. The idea was to simulate the satellite itself sending single photons to the surface.
Each pulse began its journey from Earth with about 1 billion photons and, on average, just one started the return journey. Obviously, many of the returning photons would also be absorbed by the Earth's atmosphere. So the pulse was repeated many millions of times per second.
Pan and his team say that they were able to detect the returning photons at a rate of about 600 per second. "These results are sufficient to set up an unconditionally secure QKD link between satellite and earth, technically," they add in the paper that accompanies their research.
That's a significant stepping stone. "Our results represent a crucial step towards the final implementation of high-speed QKD between the satellite and the ground stations, which will also serve as a test bed for secure intercontinental quantum communication," the team says.
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