Science
In reply to the discussion: Quantum Entanglement, Dark Counts, Coincidence Detection [View all]mindwalker_i
(4,407 posts)I'll definitely look into those IR filters - $150 isn't that much compared to the BBO or especially the detectors. I'm thinking that since I'm going to use type 1 downconversion in order to get a hight number of entangled photons, I can reflect the pump into a brick somewhere way outside the rest of the optics. And I can filter out just the degenerate photons with black plastic that has two hole in it. There will be a little bleed over, but it should be pretty minimal.
Here is a link to Cramer's initial article on the experiment. He talks about Birgit Dopfer's experiment, and how it seemed to show the interference getting destroyed by measuring the entangled photons. The coincidence detection was what people pointed to in order to argue that this couldn't be used to send information. He presented his experiment idea to a bunch of people (physicists) and nobody could give a good reason why his experiment wouldn't work in terms of physical laws. So there have been people who have looked at it and tried to poke holes in the idea.
The basic idea is to have some way of detecting when a stream of photons is still in superposition or not. Using momentum entanglement is one way of doing that - double slit or interferometer - but it would be really nice if there were an easier way, like using polarization. I'm going to have to read your post above a few times and follow the links before I understand what you are getting at.
As for the BBO crystal set, I'm aware that I don't need both for this experiment, but there may come a time when it would be useful. If, for instance, there's a way to detect when polarization is in a superposition state, these would come in handy. Who knows whether I'll get a bug up my backside to do some experiment with polarization in the future? Otherwise you are completely correct. Oh, and I wondered about the phase shift. It sounds like that isn't necessary for the 2-crystal setup, and that's good.
Anyway, you've given me a lot of good information to think about, again! I really appreciate you poking at the concepts and experimental setup because I've never done anything like this before. So thanks, again