A quantum network uses specially polarized photons to encode an encryption key—a very long series of numbers and letters that can unlock a digital file. The photons are then sent down a fiber optic cable until they reach their destination, a photon detector, which counts them, and delivers the key to the intended recipient. If the photons are interfered with, the individual packets of information are forever altered and the recipient can see the telltale signs of tampering.
via Toshiba has invented a quantum cryptography network that even the NSA can’t hack – Quartz.
Current quantum cryptography systems from companies like ID Quantique start at around $50,000, and only connect two parties at a time. “If up to 64 people can share a single photon detector than you can spread out those costs,” Shields said.
The basic idea here is that the act of measuring a quantum object, such as a photon, always changes it. So any attempt to eavesdrop on a quantum message cannot fail to leave telltale signs of snooping that the receiver can detect. That allows anybody to send a “one-time pad” over a quantum network which can then be used for secure communication using conventional classical communication.
via Government Lab Reveals It Has Operated Quantum Internet For Over Two Years | MIT Technology Review.
That may sound limiting but it still allows each node to send a one-time pad to the hub which it then uses to communicate securely over a classical link. The hub can then route this message to another node using another one time pad that it has set up with this second node. So the entire network is secure, provided that the central hub is also secure.
The team has managed to rig up a laser to fire and hit the first networked atom in a way that the atom preserves its quantum state, but also produces a photon with that information plastered onto it. The photon then shoots off down the fiber optic cable delivering it to the second atom. Network achieved. On top of that, the researchers managed to get the two networked atoms to entangle, which means the network should be completely scalable to something along the lines of an Internet.
via Scientists Establish First Working Quantum Network | Geekosystem.
NOVA series on quantum mechanics.
And another link from Cornell: Does quantum entanglement imply faster than light communication?
Say you agree to send out two beams of light to your two friends who live on opposite sides of the galaxy (you live in the middle). Ahead of time you tell them that if one of the beams of light is red the other will be blue. So you send the blue beam to your friend on one side and immediately she knows that your other friend is recieving a red beam at the same time. Aha! You say, my friends have now communicated at a speed faster than the speed of light and violated relativity, but no real information has been passed between them. You have told both of them at a normal sub-luminal speed about what you just did and that’s all. (A way of proving there’s no faster than light communication is that you could lie and send them both the same coloured beam of light and they would never know!).