Researchers from the University of Delft have taken a small but important step toward the creation of a quantum internet, the next-generation network that will connect the most advanced computers ever built.
They performed quantum teleportation between two non-neighboring nodes in a three-node quantum network. This first of its kind breakthrough is foundational in the accurate and secure transmission of information between quantum computers. Details of the achievement are reported in the journal Nature.
Quantum computers are an emerging technology poised to revolutionize complex computation, from drug modeling to the study of the universe. They can easily outperform even the most advanced supercomputer thanks to the peculiar properties of quantum mechanics – but those very properties present very unique technological challenges.
Communication between devices is among those, as sending quantum states down fiber optics would lead to lost information. To make high-fidelity transfers, you need quantum teleportation. It had been demonstrated that quantum teleportation between two nodes next to each other is possible, and this work shows that even when there’s a third node in between you can still transfer your quantum information.
The process happens like so:
Step One is the creation of the teleporter by placing the two nodes A and C (or Alice and Charlie) which are not adjacent in an entangled state. This is another fun and perplexing quantum mechanical property. The properties of an entangled state change instantaneously, even if its components were placed on the opposite side of the universe. And this change doesn’t violate relativity (but more on that in Step Four).
This is done using the in-between node B (or Bob). Alice and Bob are first entangled, and then Bob and Charlie are entangled. Then, thanks to a special measurement on Bob – something referred to as a quantum mechanical "sleight of hand" – Alice and Charlie are entangled.
Step Two is the preparation of the quantum bit, or qubit. Just like the regular bit in your computer or mobile phone encodes information, so does a qubit, but with a more quantum mechanical oomph. This is done in the Charlie node.
Once you have your qubit and your teleporter, you have Step Three: the actual teleportation. By performing a specific measurement on the Charlie node, the information there disappears – but thanks to the properties of quantum mechanics, it re-appears safe and sound in the Alice node.
This happens instantaneously, even if you could somehow place the two nodes billions of light-years away. However, information has not traveled faster than the speed of light, because the only way for Alice to get the information out of the qubit is by using the measurement result from Charlie. So Step Four is this transmission, which takes place at most at the speed of light. This allows Alice to carry out the correct operation and get the quantum information out. The teleportation worked in the Delft team's experiments.
The team is now investigating ways to switch Step One and Step Two around, as it would make more sense to first have your information and then link the systems to move it around. However, it is very challenging in quantum mechanics to store your qubits without errors accumulating.
The Quantum internet is still over a decade away, but work such as this brings forth insight into what the future of communication will look like.