By Emily Conover – Science News
Particles of light born in space have connected two cities via a quantum link about 10 times longer than any created before.
A quantum-communications satellite beamed photons to Earth, separating them by more than 1,200 kilometers. The feat showed that the particles of light can retain a strange type of interconnectedness, known as quantum entanglement, even when flung to opposite ends of a country, researchers from China report in the June 16 Science. The previous distance record was about 100 kilometers (SN: 6/30/12, p. 10). Launched in 2016, the one-of-a-kind satellite is laying the groundwork for a space-based network of quantum communication.
“It’s a huge achievement for quantum entanglement and quantum science,” says physicist Thomas Jennewein of the University of Waterloo in Canada.
Scientists have previously beamed photons up to a satellite and back again (SN Online: 6/5/16), but those particles were not entangled. Until now, no one had distributed entangled particles from space. “China is now clearly taking the world leadership in this area of quantum communication,” Jennewein says.
The technique is expected to have major technological applications. “This experiment is really important for the development of a future quantum internet,” says Anton Zeilinger, a physicist at the University of Vienna. Such a network would allow for ultrasecure communications and could connect quantum computers across the globe (SN: 10/15/16, p. 13).
An ethereal bond between two particles, entanglement is the most essential ingredient of a quantum network. Entangled particles can’t be described independently; instead, they form one unit, even when separated by large distances. Measuring one entangled particle immediately reveals the state of the other. To perform quantum communication, scientists send entangled photons from place to place. But photons can only travel so far through air or optical fibers before the material absorbs the particles, limiting the distance over which communication is possible. In the emptiness of space, however, photons can travel much farther.