[Strilanc]

The recommendation is to not use QKD. This is the correct recommendation. QKD solves key agreement if you have an authenticated line. But authentication is the harder more crucial problem.

Here's an interesting related aside: the likely design of a practical quantum internet would make QKD totally trivial. What a quantum internet would do is deliver kinda-noisy entangled Bell pairs to endpoints that wanted to communicate. The endpoints would then purify [1] this kinda-noisy entanglement into actually-good entanglement (e.g. from 1% error to 0.0000000000001% error). The purified Bell pairs can then be consumed in order to transmit qubits [2]. However, because of the monogamy of entanglement [3], the purification process must detect and correct eavesdropping (or else fail to produce output). So, once you have a sufficiently purified Bell pair, it can be measured to get a bit that can be used as a one time pad. (That said, this does still assume you have an authenticated channel! Purification requires communication, because without authentication you can be man-in-the-middle'd.)

[1]: https://en.wikipedia.org/wiki/Entanglement_distillation

[2]: https://en.wikipedia.org/wiki/Quantum_teleportation

[3]: https://en.wikipedia.org/wiki/Monogamy_of_entanglement

[SAI_Peregrinus]

Of course that also means you need a mesh network topology (every node needs a direct link to the node it wants to share qubits with), so a quantum internet (interconnected network of networks) is impossible.

[Strilanc]

That is not true. A spanning tree of physical links is sufficient to make a network where anyone can talk to anyone else.

The key ingredient here is entanglement swapping [1]. Entanglement between routers A and B can be merged with entanglement between routers B and C to form entanglement between A and C. This accumulates noise, but purification can be used at each merging step to push the noise back down to 1%.

So what transmitting a message looks like is a path between the two endpoints is selected and then entanglement swapping+purification is used to turn 1-hop entanglement into 2-hop entanglement, then into 4-hop, then etc until the entire path is spanned. Then purification+teleportation are used by the endpoints to move the message.

[1]: https://en.wikipedia.org/wiki/Entanglement_swapping