To allow for quantum communication between any two points on earth, repeaters are an essential feature in the quantum internet infrastructure. This is due to the fact that, when establishing a quantum internet link, the signal needs to be refreshed every 100 kilometres or so. The challenge has its origin in glass fibres being lossy, together with the fact that quantum mechanics dictates that qubits cannot be copied. QuTech is working on developing true quantum repeaters as we speak, and these repeaters work with the concept of quantum teleportation.
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An example of a quantum repeater in action:
Imagine a quantum link between Delft and The Hague, and another quantum link between The Hague and Leiden. Generating a link between Delft and Leiden is now possible by performing a so-called “entanglement swapping” operation: this means that the qubit in The Hague that is entangled with Delft gets teleported to Leiden. As a consequence, Leiden obtains a qubit that is entangled with a qubit in Delft: a quantum link between Delft and Leiden is established!