EDIT: 1:19 PM PST 22 December 2010 I completed this post. I didn't realize an uncompleted version was already posted earlier.
I wanted to read the quantum sequence because I've been intrigued by the nature of measurement throughout my physics career. I was happy to see that articles such as joint configuration use beams of photons and half and fully silvered mirrors to make its points. I spent years in graduate school working with a two-path interferometer with one moving mirror which we used to make spectrometric measurements on materials and detectors. I studied the quantization of the electromagnetic field, reading and rereading books such as Yariv's Quantum Electronics and Marcuse's Principles of Quantum Electronics. I developed with my friend David Woody a photodetector ttheory of extremely sensitive heterodyne mixers which explained the mysterious noise floor of these devices in terms of the shot noise from detecting the stream of photons which are the "Local Oscillator" of that mixer.
My point being that I AM a physicist, and I am even a physicist who has worked with the kinds of configurations shown in this blog post, both experimentally and theoretically. I did all this work 20 years ago and have been away from any kind of Quantum optics stuff for 15 years, but I don't think that is what is holding me back here.
So when I read and reread the joint configuration blog post, I am concerned that it makes absolutely no sense to me. I am hoping that someone out there DOES understand this article and can help me understand it. Someone who understands the more traditional kinds of interferometer configurations such as that described for example here and could help put this joint configuration blog post in terms that relate it to this more usual interferometer situation.
I'd be happy to be referred to this discussion if it has already taken place somewhere. Or I'd be happy to try it in comments to this discussion post. Or I'd be happy to talk to someone on the phone or in primate email, if you are that person email me at mwengler at gmail dot com.
To give you an idea of the kinds of things I think would help:
1) How might you build that experiment? Two photons coming in from right angles could be two radio sources at the same frequency and amplitude but possibly different phase as they hit the mirror. In that case, we get a stream of photons to detector 1 proportional to sin(phi+pi/4)^2 and a stream of photons to detector 2 proportional to cos(phi+pi/4)^2 where phi is the phase difference of the two waves as they hit the mirror, and I have not attempted to get the sign of the pi/4 term right to match the exact picture. Are they two thermal sources? In which case we get random phases at the mirror and the photons split pretty randomly between detector 1 and detector 2, but there are no 2-photon correlations, it is just single photon statistics.
2) The half-silvered mirror is a linear device: two photons passing through it do not interact with each other. So any statistical effect correlating the two photons (that is, they must either both go to detector 1 or both go to detector 2, but we will never see one go to 1 and the other go to 2) must be due to something going in the source of the photons. Tell me what the source of these photons is that gives this gedanken effect.
3) The two-photon aspect of the statistical prediction of this seems at least vaguely EPR-ish. But in EPR the correlations of two photons come about because both photons originate from a single process, if I recall correctly. Is this intending to look EPRish, but somehow leaving out some necessary features of the source of the two photons to get the correlation involved?
I remaing quite puzzled and look forward to anything anybody can tell me to relate the example given here to anything else in quantum optics or interferometers that I might already have some knowledge of.