Last month, a team of physicists led by Pan Jianwei from the University of Science and Technology in China took a major step toward the development of a quantum internet. Using Micius, the world’s first quantum communications satellite, the team was able to generate a pair of entangled photons and distribute them from space to ground stations 1200 km apart.
Entangled photons are particles of light that remain linked even when they are separated by a distance. These photons behave as a single unit, wherein changes to one photon are reflected in immediate changes to the other. Unlike other communications systems, quantum communications do not travel on a physical carrier or optical fiber from one place to another, but are essentially teleported between nodes.
This behavior makes the transmission of entangled photons particularly attractive to security experts. Without the need for information to travel between sender and receiver, it would be impossible for hackers to intercept it. In addition, an entangled photon will change when it detects its pair has been viewed or measured, allowing for the creation of encryption keys that are bound by the laws of physics, rather than code that may or may not be deciphered by increasingly sophisticated attacks. Â
A scalable quantum communications system could potentially revolutionize Internet security. However, the creation of a quantum internet will depend on the distribution of entangled photons over large distances. Previous attempts at long-distance entanglement have been limited to less than 100 km. This record was shattered by Pan Jianwei’s team last month, when entangled photons were shown to hold up at over 10 times the previous distance.
During the experiment, the team generated photons on the quantum satellite Micius, then transmitted them to ground stations located in the Tibetan Mountains, leveraging the high altitude to reduce the air and distance the photons would need to travel through. Each of the two receiving stations, located in Delingha and Lijiang, housed a telescope with a one-meter target that the photons needed to hit. During the experiment, one pair of entangled photons per second was successfully transmitted to the stations as Micius passed overhead.
Although the experiment is considered a resounding success, the creation of a practical and scalable quantum communications network is still a long ways off. Currently, transmission is only possible during nighttime due to the sun’s interference with the photons’ light signals, and the team only managed to recover one out of every six millions photons transmitted. However, Pan states that China is currently looking to build and launch additional satellites that will address these issues, and that practical applications of quantum communication may be possible within the next five years. His team has finished all designated experiments for Micius, and will soon publish the results of their findings in research journals.