Scientists Race To Establish the First Links of a 'Quantum Internet'

Actually, in a practical system, quantum teleportation would generally be used to exchange an entangled photon from which a key can be extracted, the data would sent later using a classical communication technique (like the internet) using classical symmetric encryption scheme (say, like AES-CBC). Of course if the message is small enough, you might just transport the message entangled (instead of just a way to key the encrypted message), but that's much less efficient using current QM entanglement techniques***.

Today key exchange is often done with public-private keys, but the mathematical techniques behind them rely on "trap-door" functions (functions that are relatively easy to compute, but much harder to invert). Hard != impossible, so something that is merely hard to invert today, might be easy in the future. With a quantum key exchange scheme you don't transmit the key, only an entangled photon. Thus can't invert it (with currently known physics), and you can't even intercept it (w/o being detected), so it's impossible to deduce the key even in the future. Of course you could always resort to older time-tested techniques like this [xkcd.com]...

The reason they need the satellite is to transmit the entangled photon (which is used to extract the key). A classical communications channel is effectively a cascade of store-and-forward (every amplifier and digital buffer along the way) so that every stage is making an "observation" and collpasing the quantum state. You basically want to convey the exact same photon you entangled so that the other side can receive it w/o the communication channel observing it in transit. Ideally, you'd bounce a batch of entangled photon off a satellite and the receiver gets the same photons you sent on the other side. Then both sides extract a key from their respective batch of entangled photons and use that key to exchange the message.

Of course, in a fancier system you might use that one entangled photon to quantum teleport some entangled qubits, but that would be more complicated.

***With current QM techniques, you don't really encode a pre-chosen key by somehow "entangling" it into a photon, you are basically creating a type of mind-meld (entanglement) of two photons in a way so that a quantum measurement made on one correlate with the other. With this, magically each side can extract the same information from their respective entangled photons meaning the same bit of information emerges from these measurements. That is why if someone intercepts the photon and retransmit it, both sides would know because they are unlikely have extracted the same bits from the measurments because with currently known physics it's not possible to observe and exactly recreate a quantum state (although apparently you can teleport it). If that doesn't make sense, it's because QM is not supposed to make sense, it just is (or maybe I'm not explaining it very well).

Source: http://rss.slashdot.org/~r/Slashdot/slashdotScience/~3/zVqPdtM1k24/story01.htm

Tilted Kilt Barbara Palvin Yahoo Fantasy Football Nick Foles Auguste Rodin Breaking Amish Indianapolis explosion