What’s Past is Future
“Two pairs of entangled photons are produced, and one photon from each pair is sent to a party called Victor. Of the two remaining photons, one photon is sent to the party Alice and one is sent to the party Bob. Victor can now choose between two kinds of measurements. If he decides to measure his two photons in a way such that they are forced to be in an entangled state, then also Alice’s and Bob’s photon pair becomes entangled. If Victor chooses to measure his particles individually, Alice’s and Bob’s photon pair ends up in a separable state. Modern quantum optics technology allowed the team to delay Victor’s choice and measurement with respect to the measurements which Alice and Bob perform on their photons. ‘We found that whether Alice’s and Bob’s photons are entangled and show quantum correlations or are separable and show classical correlations can be decided after they have been measured,’ explains Xiao-song Ma, lead author of the study.
According to the famous words of Albert Einstein, the effects of quantum entanglement appear as ‘spooky action at a distance.’ The recent experiment has gone one remarkable step further. ‘Within a naïve classical word view, quantum mechanics can even mimic an influence of future actions on past events,’ says Anton Zeilinger.”