To create the key, the team first had to create pairs of entangled photons. Entanglement, which Albert Einstein called "spooky action at a distance," means that the fate of one photon is tied up with the fate of the other. Measuring any quantum mechanical property of one photon automatically changes that same property in its entangled partner, no matter the distance between them.
What Einstein neglected to mention, possibly out of fear, was that at first the photons thus created think this is love. Then they get married, and then they realize the meaning of the word "entanglement"!
I'm just disappointed that it seems to happen at such a low level also. God must be a sadist :-(