Commercial quantum computers already exist, but their abilities are limited. Part of the work of building bigger and better ones—in particular, large-scale computers able to reliably correct errors and run very long computations—involves devising efficient ways to transfer quantum information. But there’s a problem: When you measure a quantum state “you alter it,” says Simone Portalupi, a quantum communications researcher and member of QR.N, a program aiming to extend the range of quantum communications. “So you can’t really clone quantum information.”
Different ways of sharing information are required, which is where quantum teleportation comes in. As a protocol for transferring quantum states from place to place without moving any matter, teleportation could become a standard way to communicate quantum information, allowing us to link together distant computers and one day build a quantum internet.
How quantum teleportation works
Entanglement is a natural phenomenon, but it can also be created artificially. And once two quantum systems are entangled, their state depends on each other no matter how far apart they are moved. This is why entanglement can be used to transmit information.
The classic example of how this works involves two researchers, Alice and Bob, who share an entangled pair of particles. In this scenario, Alice wants to send new information to Bob. She prepares a data qubit containing that information, then measures the data qubit and her half of the entangled particle pair at the same time. Known as a Bell-state measurement, this brings the data qubit into a state of entanglement with the other two, while at the same time revealing which of four states the two qubits in Alice’s possession share. At the same time it destroys the original data qubit. (More on why in a bit.)
Alice’s measurement projects the information from the destroyed data qubit, along with her half of the entangled pair, as classical information—zeroes and ones. She then texts those results to Bob along a traditional communication channel.