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Delayed choice quantum eraser by Kim et al.

  1. Oct 29, 2015 #1
    I have been looking at the results published by Kim et Al and am a little bit baffled by one of the graphs shown in fig 4. which shows the single detector counting rate of Do. The rate is very approximately constant across the whole range and averages about 280000 counts per second. Very roughly speaking this is about 10000 bigger than the coincident count.
    I'm assuming that the experiment was well shielded from external light but that light was reaching Do from the laser. If that's the case then even in low illumination I would have expected a much higher count rate when compared to the coincident counts, due to the low conversion efficiency of the BBO crystal (about one in ten to the twelve according to Wiki)
    I think the biggest problem is that the exact details of the experiment were not published. Can anyone enlighten me please or show me where to look for more details?
    Thank you
  2. jcsd
  3. Oct 29, 2015 #2


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    Would laser light that doesn't undergo SPDC necessarily reach D0? I had assumed that the lens that focuses light towards D0 would have been placed out of the path of the non-SPDC photons. Since the SPDC photons are deflected from the original laser direction, that would be possible, as long as the lens is far enough away from the BBO crystal wouldn't it?

    But even if that's right, it still doesn't explain why the curve of D0 detections in Figure 4 doesn't materially vary by location. I would have expected it to be humped.
  4. Oct 29, 2015 #3
    I think that the light that doesn't undergo SPDC is probably deflected by the Glan Thompson prism as are the entangled photons. This prism is not shown in the schematic of the Kim et al paper. Perhaps for the non SPDC photons the total deflection is not of the right value to reach the lens.
    There is a a small variation in the Do curve the count rate seeming to decrease as the Do position increases. Perhaps this should be expected due to the slightly difference in distances travelled.
    I also expected the curve to be humped and it is the apparent absence of this that prompted me to look at the numbers in the first place.
    Thank you very much for your reply, it has given me more to think about.
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