Sunday, November 15, 2015

quantum mechanics - Why does the Dopfer EPR experiment require coincidence counting?


Dopfer Momentum-EPR experiment (1998) seems to provide a interesting tweak in the EPR experiment.


To read more details on this experiment, see:




Slide 11: Dopfer Position-Momentum EPR Experiment (1998)





In summary, the experiment sends two entangled photons A and B toward two separate arms. Arm A has a lens and a Heisenberg detector, which can be placed either at the focal plane or the image plane. Arm B is sent on a two-slit filter. The observed results of this experiment are as follows:


1) if the Heisenberg detector at arm A is placed at the focal plane, the output of the two-slit filter at arm B is an interference pattern


2) if the Heisenberg detector at arm A is placed at the image plane (twice the focal plane) the output of the two-slit filter at arm B is an incoherent sum of intensities from each slit


As suggested in the 3rd paper link I posted, if you use time bins, there really doesn't seem to be any need at all to rely on the coincidence counter, as you can study the interference pattern on each time bin in isolation from photons received in other time bins


Am I confused? How is the coincidence count being used at all? notice that the interference pattern is spatial, not temporal!




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