A quantum crypto network in China

This sounds impressive: Field experiment on a robust hierarchical metropolitan quantum cryptography network. Like a lot of things in quantum information, the leap between the lab and practical real world use is a big one. What I found most interesting about this is the use of quantum routers.

As the article states, routers are needed because of the no-cloning theorem. The no-cloning theorem states that you cannot copy the state of an arbitrary quantum system. In other words you cannot do a copy and paste. You can transfer it, essentially a cut and paste, via teleportation. You cannot do the copy and paste because to copy the system you basically end up doing a measurement, which alters the state of the system.