http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser From the DCQE experiment above , assuming we could , 1. Send the idler photons on a long round trip that too a year or so before going through the double slit which is in the same lab as the detector D0. 2. Take note of each photon leaving the laser beam ( kind of tag it with a number 1.,2, 3 as they leave) 3. Send each photon at say 10 second intervals. Then say I sent a few thousand of these photons and I "Detected" them on D0 as a white block having no pattern , only a superposition of all the states ( I.E. interference and no interference patterns). But now while the idler photons are doing their round trip , I decide to Pre-select on detector D0, Only those photons that for my intensive purpose , completes a curve that looks like an interference pattern that I would want to pass through the Double slit. Once I have these Pre selected photons , I decide to direct the unselected ones away from the double slit ( since they have no use for me now), by use of some fast switching mechanism. For the preselected photons I decide to put polarisers onto the slits, to give me the which way information AND subsequently my NON interference pattern which I can detect behind the Double slit. So now I have an interference pattern at D0 but a NON interference pattern behind the double slit on another Detector , with the SAME ENTANGLED PHOTONS! What am I missing here?