From: scerir (scerir@libero.it)
Date: Sun May 12 2002 - 01:42:08 MDT
Hal Finney wrote:
> No, I don't believe this is correct, if I am understanding you. Even
> if the source were perfect and produced nothing but entangled photons,
> there would still be a problem.
>
> What we are doing on the left side is trying to measure the photon's
> position by passing it through a narrow slit. Only some photons get
> through the slit; most are absorbed by the mask. Only the ones which
> get through the slit have been measured as having a narrowly localized
> position. The remaining photons, even perfect EPR photons, are not
> localized by this measurement.
Few photons are absorbed by the mask. There are many reasons for using
D1 (detector of the 'signal beam', behind the diffraction slit or - which
is different of course - behind the interference double slit, operating
in a Geiger mode, which is a collection lens with a photodiode in the
focal spot) and D2 (detector of the 'idler beam', about 0.5 mm wide,
a fiber tip whose output is mated with a photodiode) and the coincidence
counting circuit setup (the acceptance window is few ns. wide). One is that
the 'signal beam' and the 'idler beam' *must* be orthogonally polarized
(strictly) and *must* have the same timing. If the timing is not good,
they can not even ***count*** the number of events (pairs of entangled
photons, each one in the 'signal' beam and in the 'idler' beam) and they
can not even plot the interference pattern (which, as usual, is a function
of the number of events). If we remove D1, D2, and the coincidence counting
circuit, the weird effect is still there but, of course, a big 'blurring
out' occurs.
[At least this is what I remember :-)]
s.
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