Quantum Key Exchange With an Airplane 44
submeta writes "Researchers in Munich have successfully performed a quantum key exchange between a moving aircraft and a ground station. Quantum key distribution, which exploits the phenomenon of entanglement, offers theoretically perfect encryption (although it can be vulnerable in practice). This advance is an important step on the way to key exchange with a satellite, which could enable practical usage of the technology."
Re:A little unclear on entanglement (Score:4, Informative)
No entanglement phenomenon has ever been shown (or really believed) to be capable of transmitting information faster than light. I promise you'll see it right there in the Slashdot headline if a decent experiment ever seems to show any kind of FTL information transfer.
Re:A little unclear on entanglement (Score:5, Informative)
No. It's true that you can have entangled particles far apart and measure the state of both of them at the same time. That does mean you instantaneously know what the other end would read. But that does not imply communication, since you don't have any control over what value comes out. And you can't even find out if the other end was measured or not. In such a situation it doesn't really matter which of the two particles is measured first. Measure particle one first, then the other collapses to a state consistent with the measurement of the first. Measure particle two first, then the first collapses to a state consistent with the measurement of the second. Which of the two happened depends on the viewpoint of the observer.
And actually quantum key exchange does not need entangled particles at all. There are certain optimizations, that could make use of entangled particles. But in plain quantum key exchange, you send a stream of independent particles where the sender knows the state of each particle he sends. The receiver doesn't know the state of the particles as they are received, but may learn something about the state, depending on how they are measured.
I have read of some implementations, that produce a particle in a known state by first producing an entangled pair of particles, and then measuring one of them. By the time the other particle leaves the sender it is no longer part of any entanglement. And the fact that it ever was part of an entanglement is just a minor implementation detail, that doesn't actually impact the protocol.
BB84 protocol does not use entanglement (Score:4, Informative)
This experiment implemented the BB84 protocol with attenuated coherent laser pulses (with a view to use decoy-states to close the photon number splitting attack on attenuated coherent states). The ideal implementation would use single photons (which are highly non-classical states). The protocol does not utilize entanglement. The E91 protocol was the first QKD protocol to propose using entanglement for this purpose.
Re:A little unclear on entanglement (Score:5, Informative)
I haven't studied it a lot, but have problems with a number of its claims.
Considering how difficult the field of quantum mechanics is, and how many people fail to grasp basic principles even with extensive studying of pop-sci level material, maybe a little more humility would be called for until you have a chance to read more about it.