“This type of asymmetric quantum entanglement has been predicted before on paper, but we are the first to actually create it in the lab,” study author Mehul Malik said.
To understand how truly impressive this innovation is, one must first know exactly what “quantum entanglement” really means.
Cosmos magazine has a fun way of explaining the idea of “quantum:”
“Step into your kitchen with a jar of peanut butter in your hand. You could decide to put the jar on the counter-top, or on one of the shelves above it. But you can’t put the jar between shelves – that just doesn’t make sense. In physics-speak you’d say the shelves of your kitchen are “quantised”. It just means they come in levels. In the quantum world, everything is split into levels.”
Entanglement is when two particles (in this case photons) are intimately connected so that measurement on one instantly affects the other, no matter how far away it is,
“It’s like when you were a kid and your uncle showed you a colored ball in each hand, then mixed them up behind his back. From your point of view, the two balls were “entangled” – if the red ball is in his left hand, it means the blue ball is in his right. But the quantum situation is more mysterious because the “balls” don’t have defined colors, they are color shifting – at any instant they can turn out red or blue with equal chance. It’s totally random.”
Since the 1970s, scientists have been working on ways to utilize the unique properties of quantum theory to transmit information along a secure quantum hotline. Theoretically, entanglement could be used to code sensitive information with a quantum key. Any attempt to tamper with the link and steal the information would immediately destroy the entanglement.
Physicists have managed to entangle many particles, including more than 100,000 photons. But so far the link was only symmetric – meaning it would only be useful for simple, two-party communication. In order to use entanglement for encryption, the opportunity for more interaction was needed.
Enter, the Austrian and Spanish scientists. They’ve produced a sort of “asymmetric” entanglement. This required entangling three photons in three dimensions, where all three photons are entangled, but two of them on an extra layer. The extra layer means extra communication, thanks to the twist. In this model, the photons corkscrew through the air, rather than waving up and down, as they do in traditional “2D” entanglement.
This asymmetric 3D entanglement allows for different layers of information to be shared among multiple parties. Using this method, the team of scientists have already developed a quantum cryptographic protocol, which could one day allow quantum communication to pass information along photons in different layers.
There are a number of ways this method could be applied to future communication including the opportunity for quantum computing, encryption, or even a quantum internet.
“The experiment opens the door for a future quantum internet with more than two partners and it allows them to communicate more than one bit per photon,” senior author Anton Zeilinger explained.
The method was published in Nature Photonics.