Quantum entanglement just got easier, thanks to artificial intelligence. Researchers discovered a new procedure for creating quantum links between particles, and it could be used for building quantum communication networks in the future.
This new method came as a surprise. at the Max Planck Institute for the Science of Light in Germany originally wanted to use a physics discovery algorithm called PyTheus, which he and his colleagues developed, to reinvent an experimental procedure known as 鈥渆ntanglement swapping鈥�. PyTheus is like a quantum instruction manual: tell it the properties of a particle鈥檚 quantum states that you want to create, and it outputs a procedure to make them.
But in this case, instead of spitting out a recipe for entanglement swapping, PyTheus devised a new method for entangling two particles. Krenn says he thought at first that he prompted the algorithm too imprecisely because PyTheus didn鈥檛 give him what he set out to find. But there was a big silver lining: 鈥淲e got this new way to entangle two independent particles.鈥�
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Krenn and at Nanjing University in China, who specialises in quantum communication experiments, then implemented PyTheus鈥檚 instructions 鈥� and it worked.
In quantum communication experiments like this one, information is encoded in the quantum states of particles of light, or photons, which travel through a maze of lenses, mirrors and crystals that can change those states. Making that information safe from disruption typically requires entangling photons before they are sent further on their journey. But common protocols for doing so often require using additional photons that have to be entangled themselves, making experiments more complex and difficult.
In the new procedure, PyTheus found a way to sidestep some of those additional photons. First, the researchers created two pairs of photons by shooting lasers at two special crystals, but they did so in such a way that it was impossible to tell which photon pair was created in which crystal. So, as the photons moved through the maze, the beginnings of their paths were indistinguishable. Consequently, they could undergo the quantum process of interference 鈥� where the photon pairs interact and either clash or combine 鈥� which is not possible when the photons鈥� paths are distinguishable. The team manipulated this process so that at the end of it two photons that were not originally paired up became entangled.
This method also simplified the way the researchers confirmed that the particles were entangled. They could measure the properties of only one of the photons instead of all four that were initially created. Ma says this is more convenient than more conventional entanglement confirming procedures. He says it took them about a week to implement the experiment within the set-up they already had in their quantum communication lab, but it took more than a year to perform enough checks to ensure that they could produce useful entanglement.
Now, they are assessing which quantum communication protocols may benefit most from the new procedure. Ma says quantum entanglement is a crucial resource for quantum communication networks, the predecessors of an exceptionally secure quantum Internet. It can be technically difficult to entangle two particles that are far apart and do not have a shared history, so the new procedure could make this process easier and more efficient.
at Lund University in Sweden says the method may have to be optimised further before it can be as practical as more standard protocols, but this experiment is an 鈥渆legant demonstration鈥� of established fundamental concepts in quantum physics like entanglement and indistinguishability. at the National Institute of Standards and Technology in Maryland says the new method is clever but may be difficult to scale to the level of a large communication network.
Physical Review Letters
