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matrixrising
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Recent experiments realized the thought experiment of Asher Peres on entanglement swapping. Here's the abstract.
Couldn't Alice and Bob in the experiment receive information faster than light from Victor? Here's the set up:
http://www.livescience.com/19975-spooky-quantum-entanglement.html
Victor could use this scheme to send information to Alice and Bob. Bob and Alice would be in the same place and Victor could be a mile or 5 light years away.
101100 = dog
100110 = cat
If Victor has 6 particle pairs with him, he can then send Bob and Alice the word dog or cat. Let's say he wants to send dog.
Victor would do this. He would entangle the first pair, he would choose not to entangle the second pair, he would then entangle the next two pairs and he would choose not to entangle the last two pairs.
When Bob and Alice check their particles pairs, they would see:
quantum correlations, uncorrelated, quantum correlations, quantum correlations, uncorrelated, uncorrelated or 101100 which = dog.
The beauty of this is causality will be preserved because nothing is actually moving through space-time faster than light.
This is an experiment that could be carried out today with random number generators and atomic clocks. Why wouldn't this be FTL communications?
Motivated by the question, which kind of physical interactions and processes are needed for the production of quantum entanglement, Peres has put forward the radical idea of delayed-choice entanglement swapping. There, entanglement can be "produced a posteriori, after the entangled particles have been measured and may no longer exist". In this work we report the first realization of Peres' gedanken experiment. Using four photons, we can actively delay the choice of measurement-implemented via a high-speed tunable bipartite state analyzer and a quantum random number generator-on two of the photons into the time-like future of the registration of the other two photons. This effectively projects the two already registered photons onto one definite of two mutually exclusive quantum states in which either the photons are entangled (quantum correlations) or separable (classical correlations). This can also be viewed as "quantum steering into the past".
Couldn't Alice and Bob in the experiment receive information faster than light from Victor? Here's the set up:
Both pairs of photons are entangled, so that the two particles in the first set are entangled with each other, and the two particles in the second set are entangled with each other. Then, one photon from each pair is sent to a person named Victor. Of the two particles that are left behind, one goes to Bob, and the other goes to Alice.
But now, Victor has control over Alice and Bob's particles. If he decides to entangle the two photons he has, then Alice and Bob's photons, each entangled with one of Victor's, also become entangled with each other. And Victor can choose to take this action at any time, even after Bob and Alice may have measured, changed or destroyed their photons.
http://www.livescience.com/19975-spooky-quantum-entanglement.html
Victor could use this scheme to send information to Alice and Bob. Bob and Alice would be in the same place and Victor could be a mile or 5 light years away.
101100 = dog
100110 = cat
If Victor has 6 particle pairs with him, he can then send Bob and Alice the word dog or cat. Let's say he wants to send dog.
Victor would do this. He would entangle the first pair, he would choose not to entangle the second pair, he would then entangle the next two pairs and he would choose not to entangle the last two pairs.
When Bob and Alice check their particles pairs, they would see:
quantum correlations, uncorrelated, quantum correlations, quantum correlations, uncorrelated, uncorrelated or 101100 which = dog.
The beauty of this is causality will be preserved because nothing is actually moving through space-time faster than light.
This is an experiment that could be carried out today with random number generators and atomic clocks. Why wouldn't this be FTL communications?