Scientists in Canada, US, and China have broken a new record in quantum teleportation, sending a quantum state of a particle several kilometers over a normal metropolitan fiber optic cable.

Two independent studies on the research were published in Nature Photonics (see the abstracts here and here), and provide two different but complementary approaches to the creation of Quantum Networks, which will play a crucial role in connecting quantum computers together.

Quantum teleportation doesn’t physically move any particles, but allows for the state of a particular particle to be transmitted and reconstructed away from the original.

It requires three particles – A, B, and C – with A being the particle to teleport. B and C are created in a special state called entanglement. Their properties have to be considered together rather than singularly. You can’t mess with B without messing with C too. And that’s the key to transferring the state.  

B (or equivalently C) needs to be put together with A, and a special measurement (called the Bell State measurement) has to be performed on A and B. This makes the two particles indistinguishable, but allows for the properties of A to be transmitted onto C no matter how far away B and C end up being.

You might think the difficulty of this is in the quantum mechanics, but it is actually in transmitting particle B without losing the delicate entanglement. Previous attempts have shown promising long distances of 143 kilometers (88 miles) in free space and 102 kilometers (63 miles) in fiber optics in the lab.

Comparing it to those numbers, the 6.2-kilometer (3.9-mile) transmission achieved by the Canadian-American team might not seem impressive, but it tells us that infrastructure already in use, like metropolitan fibers, can be employed in quantum teleportation.

Another advantage of the set-up is the scalability. The technology hints at quantum repeaters, which could be placed along the lines to transmit the signals further. Given better receivers, one could make the system much bigger, going from a city-wide transmission to teleportation between cities. This discovery heralds a potential new age for long-distance quantum communication.

[H/T: New Scientist]