Physics Forums

Back in October, while contributing to a thread in this forum, I ran into an interesting description of a entanglement/double slit interference experiment. One of the contributors cited a 1999 "Reviews of Modern Physics" article. This remark is made on page S290:

This experiment can be understood intuitively if we carefully analyze what registration of a photon behind a double slit implies. It simply means that the state incident on the double slit is collapsed into a wave packet with the appropriate momentum distribution such that the wave packet peaks at both slits. By virtue of the strong momentum entanglement at the source, the other wave packet then has a related momentum distribution which actually is, according to an argument put forward by Klyshko (1988), the time reversal of the other wave packet. Thus, photon 1 appears to originate backwards from the double slit assembly and is then considered to be reflected by the wave fronts of the pump beam into the beam towards the lens which then simply realizes the standard Fraunhofer observation
conditions.

Let me see if I can explain this more simply. If we call that "time reversal" photon a "Klyshko photon", then what David Klyshko was "arguing" in some other 1988 article (that I have not located) was that before the big photon reaches the down-converter and splits into two entangled little photons, a little "Klyshko photon" is emitted from the experiment to meet the big photon at the down-converter. To be clear, this is a thoroughly bizarre notion that could not possibly exist in classical mechanics - and it's not clear that the author even considers it "real". In fact, I'm not even certain that David Klyshko considered it real.

But it is testable and I would love to know if anyone has ever checked it. If you put a shutter in the apparatus so that the path of the Klyshko photo is blocked only at the moment when the Klyshko photo would be reaching that shutter, would you still be able to retrieve the interference pattern that is collected in that experiment?