China's quantum satellite makes breakthrough in secure communications

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Late previous year, the satellite, which orbits at a height between 500 and 2,000 kilometres above Earth, directed beams of entangled photon pairs at telescopes up to 1,203 kilometres apart between Delingha in Qinghai and Gaomeigu Observatory in Lijiang.

Just months into its mission, the world's first quantum-communications satellite has achieved one of its most ambitious goals.

This experiment is a big step in the new field of quantum cryptography, which makes use of quantum particles to send information securely.

Project leader Jian-Wei Pan, a physicist at the University of Science and Technology of China, proposed the project almost 15 years ago. "Many people thought it was a insane idea, because it was very challenging", he said.

Compared with previous methods of entanglement distribution by direct transmission of the same two-photon source - using the best performance and most common commercial telecommunication fibers, respectively - the effective link efficiency of the satellite-based approach is 12 and 17 orders of magnitude higher, respectively. Of the six million or so entangled pairs generated by Micius during each second of transmission, only one pair per second actually reached the ground-based detectors.

It should be noted, however, that while Micius' achievements mark a breakthrough, we're still pretty far from seeing a practical quantum network.

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The new study marks the greatest distance over which researchers have been able to separate the entangled photon pairs used to hide the encryption key, while also demonstrating that a quantum-based global communications network is actually possible, the Times said.

On Thursday, Chinese researchers accomplished a successful distribution of "entangled" photon pairs from space to the Earth. Cooperating with Micius are three ground stations (Delingha in Qinghai; Nanshan in Urumqi, Xinjiang; and Gaomeigu Observatory in Lijiang, Yunnan).

Many types of communication today use sophisticated encryption to keep them secret; most notably, financial information and other commercially- or security- sensitive communications. The team recently published their findings in the journal Science. The whole world was skeptical of its operations and future prospects. "It will be beneficial for all human beings". Using the power of entanglement scientists at the National Institute of Standards and Technology (NIST) instantly transferred information from on proton to another one 100 kilometers away in 2015. "These types of experiments are not easy to do, even within the controlled confines of a laboratory environment". The distance between the satellite and the ground stations varied from 500 to 2,000 kilometers, and beacon lasers on both the transmitters and receivers helped them lock onto each other.

Entangled photon pairs have been separated and sent to cities in China more than 1200 km apart.

With a quantum internet, messages would be transmitted by entangled particles, and any attempt to eavesdrop would disrupt the message flow and trigger an alert. The advantage of using a satellite is that the particles of light travel through space for much of their journey. Because at the quantum level, observation changes that which is being observed, the act of eavesdropping interferes with the communication itself, indicating that the messages are not secure. The latter might eventually lead to the formation of an allegedly unhackable "quantum internet" with important consequences to society and of vast geopolitical value for those government controlling it.

This figure shows a huge leap over two decades - up from a span of 144 km in 2007, and several hundreds meters in 1998 in experiments outside a lab. You have to go into space, because in glass fibres you lose the signal.

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