<p>You ought to try applying Schrodingers Cat to the
Delayed Choice Quantum Eraser. </p><p>In the dual split experiment we find that light interferes with itself like a wave and creates an interference pattern. If each photon passes through only one of the slits, we wouldn't have expected to see this interference pattern. If you slow down the emission rate until you are firing single photons at the slits, you still get the pattern. If you put in an apparatus to measure which slit a photon actually passed through, you find out that the photon travelled through either one or the other slits, but the interference pattern disappears! </p><p>In the quantum eraser, you send the photons from each slit down different paths and the apparatus to find out which path the photon took adds a certain "spin" to each photon, a different spin for each path, and the photons then hit a detector that can measure both the hit location and the spin of each photon and thus detect an interference pattern if there is one. But if the detector can tell which path the photons took you find no interference pattern, it just detects a band of light with no pattern. </p><p>Then you add an apparatus that can remove the information of which path the photon took. This is done is by removing the certain "spin" of the photon that was added by the other apparatus. You have now had a system where the photons had "which path" information, which has been removed before they hit the detector. When you turn on the eraser, the interference pattern is detected once again! </p><p>In the delayed choice quantum eraser, you add a method by which this "which path" information can be removed <strong>after</strong> the photons have hit the detector! You delay the choice of whether to erase the "which path" information until the photons have already been detected.</p><p>This is done by adding a device called a downcoverter to each path, right after the slits, that produces 2 photons from the original photon, each with 1/2 the original frequency. You can then send those photons, called the <em>signal</em> photon and the <em>idler</em> photon, along different paths. The signal photon is sent directly to a detector the and the idler photon is sent along a different path, but these photons are <strong>entangled</strong>. Using a system of different paths where the idler photons information is either erased or not, and sending them to different detectors and then correlating the data from all the detectors, you find interference patterns in the data depending on which detectors you compare to each other. </p><p>But if you set up the devices to erase the "which path" information from the idler photons <strong><em>after</em></strong> the signal photons have hit their detector, you find a hitherto undetected interference pattern hidden in the signal photon data! <strong>All</strong> the signal photons can have hit their detector and been recorded before the "which path" information is erased from their entangled idler photons, and there will be no interference pattern apparent in the signal detector data until it is finally compared to the data collected at the idlers detector. The idlers eraser could theoretically be put <strong>any</strong> distance away from the experiment, and there will be no interference pattern until the idler is erased, finally detected and correlated with the signal photons.</p><p>Is quantum entanglement subject to the arrow of time? </p><p>Here is another (in my opinion much clearer!)
description of the experiment.</p><p>How can we apply this to the cat? Well it seems to me the cat might be both dead and alive throughout its whole life.... and we won't even know for sure after it's dead!</p><em>"If you think you understand quantum mechanics, you don't understand quantum mechanics".</em> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>