Exploring Entanglement: The Limits of Influencing Quantum States

[San K]

Is it possible to force one of the entanglement "twins" to have a particular spin? or at the least increase the probability of a photon having a particular spin?

Let me illustrate with an example:

Photon A and B are an entangled pair of photons (created by striking photon C on say a BBO crystal etc).

Alice is given photon A and Bob photon B.

is there a way in which we can increase the probability (from 50% to say 60%) of Alice's photon showing spin of +? (of course the entanglement would collapse as soon as interact with A)

Simply put: even if we have just one photon (assume no entanglement) can we influence it in such a way that when we measure we get spin (+)?

if we could do that, then information could be transmitted via the (supposed/hypothetical) "phenomena" of entanglement because photon B now can be used to "read" what was done t photon A.

 

[JesseM]

No, it's not possible to change the probabilities in this way, and in fact there's a general proof that the laws of quantum field theory forbid us from using entanglement to transmit information faster than light, this proof is known as Eberhard's theorem (some other links about it can be found in [post=2068964]this post[/post]).