sci.physics.particle

Hi there

First up I'm not a physics student, I just have a weird interest in
quantum physics and string theory. As such, please forgive me if I
have totally missed the point or if the maths in the papers I'm
reading answers my question.

I've been reading up on quantum uncertain and entanglement and in
particular the "Delayed Choice Quantum Eraser" proposed by Scully and
Druhl in the early 80s. As I understand it, in that setup, you end up
with two sets of particles: particles that you can identify have
passed through slit A or B (those with "which-path information"); and
particles that you don't know which slit they passed through (those
without "which-path info"). If we look at the particles _without_
which-path info we see an interference pattern. If we look at the
particles with which-path we see no interference.

My question: if we are recording the hits of the signal photons on
photosensitive paper that is very close to the laser and the detectors
for the idler photons is a large distance away (1 light year for
example) and 364 days after the signal photons have hit the
photosensitive paper we change the configuration of the beamsplitters
and mirrors such that we lose all which-path OR such that we get which-
path info for all signal photons, what is the pattern on the
photosensitive paper?

Using the diagram here:
http://en.wikipedia.org/wiki/Image:Kim_EtAl_Quantum_Eraser.svg
or Fig 2 here:
http://xxx.lanl.gov/PS_cache/quant-ph/pdf/9903/9903047v1.pdf

We setup such that:
- The distance to the Glen Thomas prism was 1 light year
- The D0 detector is replaced with photosensitive paper
- 364 days after we start up the laser, the BSa, b, c are removed
(which-path now available for all photons) OR BSa, b, c obstructed (no
which-path info at all)

I hope that's not too stupid. I'm just having trouble getting my head
around it.

Actually, thinking about it, in either of those cases, I think you end
up with one step back and just a delayed choice experiment.

Anyway, I'll post and hopefully someone can get my brain to comprehend
what's going on.

Thanks

Andrew