<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>That's right. The original photon is "down-converted" into two entangled photons with half the frequency, after it has passed through the slit. One of those entangled photons, the "signal" photon, is sent directly to a detector screen whilst the other one, the "idler" photon, is sent along a separate path for each slit, thus the "which path" information for the "idler" photons exists. The "signal" photons do not make an interference pattern at the detector, as their entangled photons have "which path" information.If you detect the idlers with "which path" information and correlate the hits on their detector with the hits on the signal photon detector, you find no interference pattern, but if you erase the "which path" information for some of those idler photons before they hit a detector, so the detector cannot know which slit the idler photon corresponds to, you find that if you correlate the hits from the detectors that recieved "erased" idler photons with the hits on the signal photon detector, those entangled signal photons did indeed hit their detector in the correct place to make an interference pattern. The interference pattern was hidden in the data and can only be revealed once you have the information from the detectors of the erased idler photons, and the choice as to whether to erase the "which path" information or not doesn't need to happen until after all the signal photons have hit their detector. This seems to imply that quantum entanglement works backwards in time, but you cannot transmit information backwards through time as you can only correlate the information at the speed of light, after the idler photons have been detected. <br />Posted by SpeedFreek</DIV></p><p> </p><p><font size="3" color="#0000ff">Ok, I have read everything I could find on this and I have some observations. Either I'm missing something, or they are rigging the experiment( perhaps unintentionally) and are then surprised when the results reveal that. Do you agree with the following? First, the way its set up, its a wonder that it works at all. Since the original photon, the one that goes through the slit, is absorbed to produce two new ones. it cannot produce an interference pattern, or any other pattern. Next, the signal photon is sent to D0. Since, by definition, an interfered photon will follow a different path from an uninterfered one, how can this one receptor determine the pattern? Am I correct that no actual pattern is generated, rather the pattern is inferred from the assumption outlined here:</font></p><p><font size="3" color="#ff0000">At this point, it is possible to correlate the which-way information of these two groups of photons with the corresponding subset of photons detected at D0. We could paint eg in violet all hits at D0 corresponding to hits at D3 or D4, and we find that their distribution has no interference (<strong><u>according to the fact that the which-way information is known</u></strong>). We could then paint in red all hits at D0 corresponding to hits at D1, and in blue those corresponding to hits at D2, ie. after the erasure of the which-way information, and we find that their distribution shows two interference pattern, one with fringes for D1 and one with anti-fringes for D2, which cancel when added together.( <font color="#000000">from the article entitled</font>
The quantum eraser experiment 
</font></p><p> </p><p><font size="3" color="#0000ff">If so, then its no surprise that the data is actually computer generated and the principal of GIGO reveals the answer to the riddle.<br /></font></p> <div class="Discussion_UserSignature"> </div>