By entangling particles on a satellite and shooting them down to Earth, China may have just set the tone for a global “quantum space race.”
In a new study in the journal Science , Jian-Wei Pan, a physicist at the University of Science and Technology of China in Shanghai, and his colleagues report that they were able to entangle photons aboard a satellite 300 miles above Earth and then beam those particles to three ground stations across China—each separated by more than 700 miles.
It’s an unprecedented feat. Not only were the particles entangled in space (scientists have never done this before), but they retained their bizarre connection even after they’d been separated by a distance 10 times the previous record for what’s called “quantum teleportation.”
Entanglement still boggles physicists’ minds to this day, even though our understanding of it has its origins in the renaissance of early 20th-century quantum theory research. According to quantum mechanics, particles can be in different “states” at once, and when they’re observed, those superimposed states collapse into just one. When particles are “entangled,” their states are linked together across space—when the one particle is measured, the other particle’s properties become frozen as well. Einstein wasn’t a fan of this idea because it suggested that communication between particles could travel instantaneously—i.e., faster than the speed of light.
Though it sounds like a pointless exercise to make “twin” particles and send them careening away from each other, scientists are doing just that in order to pioneer what’s called “quantum communication,” an ultra-private way of sending messages. Because observation of one entangled particle immediately affects its partner, information sent via quantum methods can’t be hacked without it being very obvious to the other party involved.
Here’s Sarah Kaplan, reporting for The Washington Post:
But until Pan and his colleagues started their experiments in space, quantum communication faced a serious limitation. Entangled photons don’t need wires or cables to link them, but on Earth it is necessary to use a fiber optic cable to transmit one of the particles to its desired location. But fibers absorb light as the photon travels through, so the quantum connection weakens with every mile the particle is transmitted. The previous distance record for what’s known as quantum teleportation , or sending information via entangled particles, was about 140 kilometers, or 86 miles.
But no light gets absorbed in space, because there’s nothing to do the absorbing. Space is empty. This means that entangled particles can be transmitted long distances across the vacuum and not lose information. Recognizing this, Pan proposed that entangled particles sent through space could vastly extend the distance across which entangled particles communicate.
Tests on the ground confirmed that the particles sent from the Micius satellite were indeed still entangled. Eventually, Pan wants to use the satellite for more complicated quantum communication; others working on this area of research hope that eventually, a “quantum internet” could allow for super-fast and super-secure communication around the world.
Photo credit: A. Fujii, NASA