Re: FTL by Down-converting (Revised)
From: Horace Heffner (hheffner_at_mtaonline.net)
Date: 10/30/04
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Date: Sat, 30 Oct 2004 13:10:57 +0000 (UTC)
The following discussion of the subject faster than light (FTL)
communication method, FTL by down-converting (Revised), is intended to
shed some light on the design assumptions and places where I may have
flawed thinking.
A 1-1 photon-idler coincidence counting is vital to the Kim et al [1]
experiment, on which the FTL by down-converting method is based, because
that experiment is set up so that the paths of only about 50 percent of
the idlers is known. In the Kim experiment Bob can not see an
interference pattern at all, but when the photons are considered on an
individual basis, the signal photons corresponding to the idlers (via
recorded data) which are "observed" do not make an interference pattern,
while those whose histories are "erased" by the configuration in Fig. 1 do
make an interference pattern. It is a fundamental assumption of the
method that by knowing or not knowing the histories of 100 percent of the
particles Bob must clearly be able to distinguish a bimodal or
interference pattern accordingly, without knowledge of the timing or the
need for coincidence counting. If Bob dutifully records his
distributions, and 100 percent of the photons are affected by a quantum
wavefunction that generates interference, then he must be able to see that
interference pattern because there are no photons left to mask it out.
There is no need for a later comparison with Alice, and thus no need for
Bob to record at all, other than to discriminate between the two patterns.
The significance of the Kim et al experiment is that *individual idler
photon histories can be wiped out* by scrambling that idler's history with
other histories by injecting the idler into the *beam* from the opposed
path. (There doesn't even have to be a particle-particle interaction, it
is merely the fact that the origin of the mother photon becomes uncertain
that does the trick. Truly incredible!) Fig. 1 shows how an idler from
one beam can be (was) mixed into another idler beam, scrambled, so as to
lose its history.
Full Mirror
R1--->-------------\
|
| Half Mirror
L1---->------------\----------------------DL
|
|
DR
Fig. 1 - Alice's which-path scrambler
Note that ascii figures require a fixed font, like Courier. Microsoft
Outlook users may need to select "fixed" in the "textsize" submenu of the
"view" menu.
The fact that detector DR and DL can not determine whether an idler came
from R1 or L1 in Fig. 1 *erases its history* and permits the
corresponding signal photon to experience the quantum wavefunction for
interference. DL detects half its particles from R1 and half from L1, as
does detector DR. When the corresponding signal photon pattern is tallied
for all the photons detected by DL and DR, an interference pattern is
observed. The history of *every* photon passing through the scrambler
thus must be erased, even those which pass straight through the
half-mirror, i.e. Alice's beam splitter. The scrambler in Fig. 1 can be
repeated in series if necessary to compensate for imperfect beam splitting
ratios, imperfect beam overlap, and other problems.
The suggested method is a bit unusual because instead of utilizing an
instantaneous wavefunction collapse to achieve FTL it relies heavily on an
instantaneous *wavefunction resurrection.* By erasing the history that
destroys the wavefunction, the wavefunction is instantly resurrected, and
thus the interference is projected at faster than the speed of light,
instantaneously, to Bob's location.
Fig. 2 and the following discussion sums up the critical issue for the
proposed experiment design in a nutshell.
DL
|
| Alice in
| "erase history"
^ mode
R1 |
/------------->----------//----->------->DR
| |
^ ^ L1
| |
... to Alice ... to Alice
| |
| |
R1 | laser |
| | | Legend:
^ v ^
| | | / - mirror
| R | | // - splitter
/----X----<----// Charlie | X - down-shifter
| | | o - pattern detectors
| v L | DL,DR - photon detectors
v | L1 |
R2 | X------>--------/
| |
...to Bob ... to Bob
| |
| |
v v
o| | L2
o |
o------<------/
o
Bob's Pattern
Fig. 2 - Experiment with Alice in 100 % "erase history" mode.
The issue of whether the suggested experimental arrangement is capable of
information transfer or not boils down to whether Bob sees an interference
pattern in the configuration diagramed in Fig. 2 or not (assuming path
lengths are all adjusted properly). If he does, then the experiment must
in fact be capable of transmitting information FTL, because it is well
known that which-way knowledge, for example obtained by eliminating
Alice's splitter, and thus directing R1 to DR and L1 to DL, eliminates
Bob's interference pattern. Alice thus has numerous physical means
available to switch from interference mode to bimodal mode. The
(experimental) reason Bob should see the interference pattern is that
every "history erased" photon entering Bob's detectors in the Kim et al
experiment contributed to the interference pattern. Since 100 percent of
the photons are "history erased" by Alice in Fig. 2, Bob should clearly
see the interference pattern. This is the fundamental assumption of the
design and the most likely conceptual error.
Causality and relativity arguments that the suggested method cannot
achieve FTL communications are not germane, despite the fact they are
likely correct, because relativity and its related causality problems are
the very things tested by the proposed method. Though FTL communication
may indeed be impossible, it is hoped the subject method can reveal
something about the nature of quantum events. Corrections to errors in
the underlying assumptions would be appreciated.
References:
[1] Kim et al, Phys. Rev. Lett., Vol 84, no. 1, pp 1-5
Regards,
Horace Heffner
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