A team of researchers set a record for quantum “teleportation” this week.
In a first, scientists “teleported” information from Earth to space over a distance of over 300 miles. Previous experiments had done the same from space to Earth and over shorter distances. Photon “teleportation” can enable long-range data encryption, and would be vital to a large-scale quantum computing network. But this doesn’t mean we’re ready to beam objects up to space.
This transfer relies on the principle of entanglement, by which two particles are connected (regardless of distance) in that measuring one correlates to the state of the other. Using entanglement, the quantum state of a particle can be transferred to another, so it essentially assumes the identity of the other particle, much as we envision physical teleportation.
In an interview with the BBC, Oxford professor Ian Walmsley explained that the team communicated information by harnessing the laws of quantum mechanics. They transferred information from a photon on Earth to a second photon up in a satellite, but did not physically send the first photon anywhere.
Ryan Mandelbaum explains this phenomenon for Gizmodo:
So, here’s a simplified version of quantum teleportation. Let’s say you take a red and a green ball, put each randomly into one of two bags, and hand one bag to a person on the ground, and another to a person at the satellite. But on the ground, there’s a second bag, containing another green ball that the folks on the ground want to “teleport” to the satellite, without anyone else knowing it was green. Quantum teleportation says that, with the entangled link already set up, the folks on the ground have only to open both of their bags, then call the satellite on the phone and say either “same” or “different.” If the ground observer opens both bags and sees both balls are green, she can just say “same” to the satellite. The satellite will then open his entangled bag, which has to have a red ball, which means the ground must have had the green ball in the entangled bag, and that means the secret ball had to be green.
Thus, the state of the secret ball is “teleported” to the satellite.
In previous attempts, achieving great distances was challenging. Entanglement is fragile and easily disrupted as photons interact with matter over longer distances. Scientists have tested models of a quantum network by transmitting information through optical fibers, but the team from University of Science and Technology of China led by Chao-Yang Lu demonstrated much greater distances by using the vacuum of space, which has few particles with which the entangled photons might interact.
Over the course of a month, the researchers sent millions of photons between the ground station and the Micius satellite, a sensitive photon receiver that reads information from photons on Earth. The ground station was placed at a high-altitude site in Tibet at over 13,000 feet above sea level to minimize disturbance from the atmosphere, which can disentangle photons. Over 900 of the transfers were successful. Based on satellite orbit, the photons were separated by between 310 and 870 miles.
The “teleportation” process transfers qubits, or quantum bits of information. A quantum network would use entangled photons to share information. Measuring their state—the data encoded in the photon—would immediately disturb them. Thus, any attempts to read or interfere with messages outside of the receiver would instantly be detected.
“This work establishes the first ground-to-satellite up-link for faithful and ultra-long-distance quantum teleportation, an essential step toward global-scale quantum internet,” the team wrote in this week’s paper.