From: Hal Finney (hal@finney.org)
Date: Fri May 10 2002 - 14:06:15 MDT
If you are using a polarizing beam splitter, and the photons are in the
entangled state, then the arms taken by the two photons will be the same
if they are measured.
However, as I showed in my long reply earlier, you will not be able
to get interference in this case, even if you don't measure them.
Basically it is because the two paths are distinguishable.
If you use a non-polarizing beam splitter, where it is random which path
is taken, then the arms taken by the two photons will not be the same.
Each photon will interact with its beam splitter separately. The fact
that the photons are entangled in their polarization state will not
imply that they behave identically when interacting with separate half
silvered mirrors.
In this case you will always see interference, regardless of what you
do to the other system.
So I think in the one case you will never see interference, and in the
other case you will always see inteference. Either way you will not
be able to send a message.
Hal
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