China has sent an unbreakable code from its satellite to the Earth, laying the foundation for building a hack-proof global quantum communication network, official media said on Thursday. Typical encryption relies on traditional mathematics and while for now it is more or less adequate and safe from hacking, the development of quantum computing threatens that. Pan Jianwei, lead scientist on the experiment from the state-run Chinese Academy of Sciences, was quoted by the state media saying that, during that time, 300 kbit secure keys are both generated and sent.
The message was sent via quantum physics, which means that if anyone were to eavesdrop on the communications, it would result in detectable changes and alert the receiver and sender that the communication had been compromised.
"Any eavesdropper on the quantum channel attempting to gain information of the key will inevitably introduce disturbance to the system, and can be detected by the communicating users", the researchers further stated. But, it was restricted by distance.
The satellite, called Quantum Experiments at Space Scale (QUESS), is claimed to be the world's first of its kind, and was sent into a sun-synchronous orbit on August 16, 2016.
One way to improve distribution lies in the protocol of quantum repeaters, whose practical usefulness, however, is hindered by the challenges of simultaneously realizing and integrating all key capabilities.
The technology is already used for terrestrial communications via fibre optic cables but with a big practical limit.
"Satellite-based quantum key distribution can be linked to metropolitan quantum networks where fibers are sufficient and convenient to connect numerous users within a city over 100 km". The transmissions were made from distances that varied from 645 km to 1,200 km.
Due to the fact that the entangled photons can not be amplified as classical signals, new methods must be developed to reduce link attenuation in satellite-to-ground entanglement distribution.
This use of entangled photons is nothing new.
The quantum key transmission rate between the satellite and the ground was up to 20 orders of magnitude more efficient than an optical fibre of the same length.
With the use of the satellite, Chinese researchers at the Quantum Experiments at Space Scale (QUESS) project, were able to transmit secret messages from space to earth at a further distance than ever before.