steveb3210 writes "Physicists have demonstrated that making a decision about whether or not to entangle two photons can be made after you've already measured the states of the photons."
Here's the article's description of the experiment: 'Two independent sources (labeled I
) produce pairs of photons such that their polarization states are entangled. One photon from I
goes to Alice, while one photon from II
is sent to Bob. The second photon from each source goes to Victor. Alice and Bob independently perform polarization measurements; no communication passes between them during the experiment—they set the orientation of their polarization filters without knowing what the other is doing. At some time after Alice and Bob perform their measurements, Victor makes a choice (the "delayed choice" in the name). He either allows his two photons from I
to travel on without doing anything, or he combines them so that their polarization states are entangled. A final measurement determines the polarization state of those two photons. ... Ma et al. found to a high degree of confidence
that when Victor selected entanglement, Alice and Bob found correlated photon polarizations. This didn't happen when Victor left the photons alone.'