# PHYS; Quantum Teleportation

John K Clark (johnkc@well.com)
Fri, 12 Dec 1997 23:12:55 -0800 (PST)

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On Fri, 12 Dec 1997 Dan Fabulich <daniel.fabulich@yale.edu> Wrote:

>Yes, you can't understand the message unless we have a mutually
>known key... But if I'm only sending you one of two messages, 0 or
>1, then we can both "know what the message I want to send you is,
>" having agreed upon that subluminally, but then use this agreement
>to send superluminal communication.

Ok, there are 2 entangled photons, one headed toward me and the other one
headed toward you a billion light years away. We previously agreed that if a
photon makes it through your polarizer, set at 0 degrees, that means I'm
telling you to attack by land, if the photon doesn't make it through your
detector that means attack by sea. A billion years after we separate I decide
you should attack by sea, so I set my polarizer at 90 degrees. If my
entangled photon gets through my polarizer at 90 degrees then there is a zero
probability that your photon will get though your polarizer at 0 degrees,
so I've sent a message to attack by sea and done it much faster than light
and everybody's happy. There is just one problem, how can I make sure that my
indeterminate entangled photon does in fact get through my detector when I
set it at 90 degrees?

When a photon of indeterminate polarization arrives there is always a 50%
probability it will get through, regardless of the direction I set my
polarizer at, there is just no way around it. If my photon is absorbed by my
polarizer set at 90 degrees, and there is a 50% chance it will be, then there
is a 100% probability your photon will be transmitted through your polarizer
set at 0 degrees, and that would give you the erroneous message to attack by
land. Flipping a coin would work just as well for you, and it would be a lot
easier.

John K Clark johnkc@well.com

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