Lets say you have two entangled particles (A,B) and you already measured theirs spins and know that A has z+ and B has z-

What will happen if after the measurement you will set the spin of B to z+ (don't know if this is possible, but lets say that yes), will the spin of A change to opposite?

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    $\begingroup$ If $A$ is in the state $z^+$ and $B$ is in the state $z^-$, then the pair is in state $z^+\otimes z^-$, which is (obviously) not entangled. $\endgroup$ – WillO Sep 4 '15 at 1:54

No, but you can't really do that pre-measurement when they are entangled either.

See ("FTL" Communication with Quantum Entanglement?) for a more-general explanation I recently did about what quantum entanglement is; it may help demystify the basic idea of what entangled systems do together.


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