Possible Breach or Quantum Voodoo?

Mission 4: Entanglement. Part of the Quantum Courier Service, a free course from the Oxford University Quantum Information Society.

We have a situation. Agent Alice is in the Clarendon Lab; Agent Bob is on a satellite over Mars. To test our secure lines we flash a random question at each of them at the same millisecond. Each of them independently gets one of two questions, and each gives one of two answers.

Here is what has Internal Affairs losing its mind. Take Bob's answers on their own and they are a perfect coin flip; nothing to see. Take Alice's on their own, same. But line the two columns up afterwards and the pattern of agreement is too strong. Not “they always match”, because a pair of pre-agreed codebooks could do that, and we checked, they don't have one. Too strong for any pre-agreed anything. There is a hard mathematical ceiling on how well two separated parties can agree if they packed their answers in advance, and Alice and Bob are sitting above it.

Mars is 12 light-minutes away, so nobody is phoning ahead. They aren't cheating. They are using something much weirder. Welcome to the crown jewel of quantum mechanics: Entanglement.