A team of Chinese scientists succeeded in tests that distributed entangled paired photons over 1,200 kilometers, using the Quantum Experiments at Space Scale (QUESS) satellite. The QUESS mission was launched in August 2016, and has since received plenty of attention around the globe. It is the first satellite built to carry out quantum communications, the most secure way of transmitting information.
An artist’s impression of quantum entanglement at a long distance. Credit: Victor De Schwanberg/SPL
Quantum entanglement is a phenomenon described by Albert Einstein as "spooky action at a distance", due to its confounding nature according to the laws and theorems of classical physics. To put it in a simple way: two entangled particles use mysterious connection to affect each other instantly even when they are far apart; or your twin sibling in New York feel a simultaneous buzz when you are sipping coffee in Seattle. The reason why communication based on quantum entanglement is secure is because any eavesdropping would interfere with entanglement of the particles that carries confidential information. Therefore it has been claimed as a hack-proof method to communicate.
QUESS Quantum Optic Experiment. Credit: Xinhua/Chinese Academy of Sciences
On GUESS, researchers split a beam of photons that share a quantum state. The entangled photons were then transmitted separately to two ground observatories through two onboard telescopes. Once the particles arrived, the team immediately examined the photons’ quantum state. Results showed that the photons remained entangled even though they were over 1,200 kilometers (746 in miles) apart - a record breaking distance. What is more, the link efficiency was many times higher than optical fibers transmission.
The reported QUESS experiment is a Bell test (named after the physicist John Bell). It is designed to demonstrate the real world existence of certain theoretical consequences of entanglement as defined in quantum mechanics, which otherwise is not supposed according to Einstein’s principle of local realism.
Related reading: Bell test
“This satellite-based technology opens up bright prospects for both practical quantum communications and fundamental quantum optics experiments at distances previously inaccessible on the ground”, said Pan Jianwei, a member of the Chinese Academy of Sciences and the main architect of QUESS.
Source: Nature/People’s Daily