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Let us say Alice wants to communicate state |T> (also a qubit) to Bob. Given, they have an EPR Pair shared amongst them. Alice interacts her qubit with |T> and then sends the measured state (classical information) of qubits to Bob. Depending upon the measured state of qubits(00,01,10,11) Bob uses the quantum gates to get back |T>. But instead of doing that Bob could have decided upon using a particular quantum gate. So, he could have got the right information with a probability of 0.25 but at least he could have achieved faster than light teleportation with a probability of 0.25.


marked as duplicate by Norbert Schuch, peterh, John Rennie quantum-mechanics May 14 '17 at 6:33

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    $\begingroup$ So, you have something that is in one of four states, I guess the state, and I'm right with a probability of 1/4. $\endgroup$ – tfb May 13 '17 at 9:18

No, it can't.

This is no different than trying to retrieve tomorrow's newspaper by generating a random page. Even if you got really really absurdly lucky and generated the correct page, flipping coins doesn't make you a time traveler.

If Bob is just going to randomly guess what the fixup operations are, why even bother with the teleportation? There's no need to pre-share EPR pairs or have Alice do Bell measurements... just have Bob prepare a bunch of random qubits and assume they're the message Alice wanted to send.

The only thing the teleportation protocol adds on top of just-use-random-qubits is heralding: Alice's measurements can tell you if Bob's guesses were right. But in order to use the heralding Bob has to wait for Alice's results to reach him (so he knows whether to put the run in the "guessed right" bucket or the "guessed wrong" bucket). So the process is still not instantaneous.


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