[extropy-chat] Send your future self an email

scerir scerir at libero.it
Wed Mar 31 21:44:55 UTC 2004


[the trio Zeilinger, Elitzur, Dolev wrote]
"Entanglement occurs by creating indistinguishabilility
between the two mutually exclusive histories of the photon."

[Natasha]
Sounds like the photons had a Rashomon experience.

Haha! We can also add "indistinguishability" and "histories",
if not "entangled", to this piece of poetry by John Bell ...

"The following words
have no place
in a formulation
with any pretension
to physical precision:
system, apparatus,
environment, microscopic,
macroscopic, reversible,
irreversible, observable,
information, measurement ..."
(also in "Against Measurement",
Physics World, August 1990)

But imagine that you have two "atoms":
A and B, situated in distant locations,
both in an "excited" state |0>.
These atoms may both decay to the state |1>,
due to spontaneous emission, thus producing
one "photon" ("photon" is not on that list,
by Bell, but it is something still unclear,
in the literature).

A (360°) detector is placed at half way,
between the two atoms. After some time
the dectector "clicks". But we cannot
"distinguish" (that's the word!)
from which atom the detected "photon" came.

We have produced the following "entangled" state:
|psi> = |0>_A |1>_B + |1>_A |0>_B)   [*]

The point here is the impossibility to determine,
from the detection event, which atom
emitted the "photon".

Hence ... entanglement occurs by creating
"indistinguishabilility" between two mutually
exclusive histories of the photon.

[*]
or |psi> = 1/sqrt2 (|0>_A |1>_B + e^(i phi)|1>_A |0>_B)
where phi is a fixed "phase".






More information about the extropy-chat mailing list