Science
In reply to the discussion: Quantum Entanglement, Dark Counts, Coincidence Detection [View all]mindwalker_i
(4,407 posts)I'll go through those at some time soon.
I built a Mach-Zehnder interferometer and got that working, then added a couple of galvonometer set - they're used in laser animation to rapidly move the beam around and draw stuff - and sent the output beams to detectors. I'm still using visible light at intensities that can be detected by the three-terminal detectors from somewhere way above in this post. I could get a good pattern on an oscilloscope with this configuration.
The main problem was that I couldn't precisely adjust things. Every time I tried to move one part of the system, the others would get all screwed up, making it really difficult to carefully adjust mirrors and prisms to get solid interference patterns. So I started working on designing and building mounts for the optics. I've got pieces of a design that are starting to work, and am figuring out how to actually machine pieces. This is tough because I'm definitely not a machinist, and am learning everything as I go.
The interference pattern gets disturbed when my cats walk by. Even with the whole thing suspended on springs, it's incredibly sensitive to vibrations.
I have the BBO crystal (cut for colinear parametric downconversion) and the single photon detectors. The circuitry to count photons works, and interfaces to Linux through USB. I've made some progress building printed circuit boards - I really need to get this thing off of breadboards. However, I haven't actually done any downconversion yet. I need to build a mount for a dichroic mirror to reflect off the violet light after downconversion, and I need to build some blocks to only allow precise parts of the interference pattern to get to the detectors. More machining.
As for the ideas behind the experiment, those are still open. I have heard from Cramer that he is working with Zellinger, and he refers to some unpublished experimental results that Zellinger has that relate to this whole thing. I don't know what those are, but Cramer seems to be happy about it, and I doubt that it shows Cramer's experiment won't work. I still have this feeling that, if for some reason Cramer's experiment didn't work, one would be able to get an interference pattern AND measure the path of each photon. So something has to break - either you can actually get the which-way info and interference, or you can send information through entanglement. Give me FTL or Heisenberg's uncertainty principle gets its ass kicked.