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CHINESE RESEARCHERS have sent entangled photons from a satellite to two ground stations 745 miles apart. This distance is by far a new record for what Einstein called “spooky action at a distance.”
Remember quantum entanglement? My favorite description of this oddity of modern physics involves two pals Alice and Bob. Image they have two electrons that are entangled. That is, their electron spins are correlated, with 50/50 probability of being up or down.
Suppose Alice measures her electron and discovers it is spinning upward. Then, in theory, regardless of how far apart she and Bob are, she knows instantly that his entangled electron is spinning downward.
Back in 2015, researchers in the Netherlands confirmed this theory in practice, at a distance of 0.8 mile. Spooky, even at this modest distance.
The Chinese achievement increases this real-world distance to 1200 kilometers/745 miles, though it took some complexity to do it. One challenge is that entangled photons degrade rapidly as they pass through air or optical fibers of transmission. Instead, researchers employed China’s Micius satellite, named after an ancient Chinese philosopher scientist.
The Micius satellite was launched in August 2016, its mission focused on photon-entanglement research. “Spooky Action Achieved at Record Distance,” by Gabriel Popkin is described in Science, June 16, 2017, published by the American Association for the Advancement of Science.
Popkin writes, “In their first experiment, the team sent a laser beam into a light-altering crystal on the satellite. The crystal emitted pairs of photons entangled so that their polarization states would be opposite when one was measured. (Think Alice and Bob, only in Mandarin.)
Photon pairs were then split and sent to separate receiving stations, Delingha, Tibet, and Lijing, Yunnan, 745 miles apart, both high in the mountains.
Popkin notes that photon degradation caused by passing through the air is minimized by this sending from satellite and receiving at high altitude. Researchers measured more than 1000 of these photon pairs and found their opposite polarizations to be far more than might be expected by chance.
Thus, spooky action at a distance has been confirmed again, this time at a distance of 745 miles.
A future experiment will test efficacy of this technique on an intercontinental basis: One of the stations will be in China, the other in Austria. Among its challenges is holding half of the entangled photons aboard the satellite until Austria comes into view.
There’s a lot more here than mere record-setting. At the heart of quantum entanglement is a potential for utterly secure, completely unhackable communication. In Alice and Bob terms, suppose each of them possesses an entangled “quantum key.” If Eve, an eavesdropper, attempts to intercept a quantum-encrypted message, this disrupts the shared key and alerts Alice and Bob to Eve’s skullduggery.
A great deal of research is left to do. As one example noted in Science, the Chinese achievement “recovered only about one photon out of every 6 million sent from the satellite—far better than ground-based experiments but still far too few for practical quantum communication.”
Nevertheless, Science says this current work “shows China’s growing mastery of both the quantum world and space science.” For example, consider the successful targeting of photon beams from a satellite orbiting at nearly 5 miles/second (18,000 mph) more than 300 miles above the ground stations.
“Other countries are inching toward quantum space experiments of their own,” Science notes. “The Canadian Space Agency recently announced funding for a small quantum satellite. European and U.S. teams are also proposing putting quantum instruments on the International Space Station.” Also noted is a joint project of Australia and China in sending quantum information between two satellites.
Austrian researcher Anton Zeilinger has urged the European Space Agency to launch its own quantum satellite. He says, “I’m personally convinced that the internet of the future will be based on these quantum principles.”
Do you suppose the primary language of this new internet might be Mandarin? ds
© Dennis Simanaitis, SimanaitisSays.com, 2017