Re: IBM Breakthrough?

[mpd@netcom.com (Mike Duvos)]

John Young <jya@pipeline.com> writes:

 > IBM has an ad in the Feb 26 New Yorker where a joker e-
 > mails a recipe-swapping friend in Osaka that "I'll teleport
 > you some goulash." The text then states:

 > Margit is a little premature, but we are working on it.

 > An IBM scientist and his colleagues have discovered a way to
 > make an object disintegrate in one place and reappear intact
 > in another.

 > It sounds like magic. But their breakthrough could affect
 > everything from the future of computers to our knowledge of
 > the cosmos.

 > What is this breakthrough or is it just a chump tease?

The ad overstates the result a bit. :)

You may recall, a few years back, that there was some interest in
the possibility that the non-local collapse of a quantum
mechanical wave function could be used to transmit information in
violation of causality, that is, faster than the speed of light.

The central idea was this.  You generate a system consisting of
two things whose wavefunctions are correlated, and after they
have separated some distance, you perform a measurement which
collapses the wavefunction of one of them and yields some result.
This might be the polarization of a photon, the spin of a
particle along some axis, or where on a photographic plate an ion
will strike after passing through a Stern-Gerlach device.

Since the wavefunctions are correlated, you now know the exact
same information about the twin system and have collapsed its
wavefunction non-locally without directly performing a
measurement on it.  This general notion is known as the
Einstein-Podolsky-Rosen(EPR) Effect, and measurements of
canonically conjugate variables on branch systems having a
spacelike separation give a unique result according to Quantum
Mechanics which is distinct from the classical case and which
requires this superluminal transmission of wavefunction
information.

Now actually building an apparatus which does such a thing is
tricky, since light moves pretty fast, but a few years back, this
result was experimentally confirmed with a device that produced
photons with correlated spins moving in opposite directions, and
managed to make measurements that were instantaneous enough to be
spacelike in separation.

Unfortunately, the scientists found that there was no way to use
the EPR Effect to transmit information, since although the
measurements made had a correlation, you needed the information
from the original system to decode the output of the other in a
meaningful way.

Now on to IBM's result.  Although the EPR Effect cannot be used
to transmit information (read the results of measurements), it
can be used to transmit mixed quantum states, which an attempt at
measurement would destroy.  So if you haven't measured something,
and it's value is indeterminate for a system, then you can tunnel
that unmeasured something anywhere else using the EPR Effect and
measure it there.

The general method for such teleporation is as follows.  You
create an "entangled" pair of particles whose wavefunctions are
perfectly correlated and unmeasured.  One interacts with the
particle to be teleported and the other at some distance
interacts with another identical particle to which you wish to
transfer the state of the first.  Everything is arranged so that
the state of the teleported particle is destroyed by interaction
with the first of the pair of particles, and it twin, perfectly
correlated with the first and inheriting its state via the EPR
Effect, transfers that captured state to the copy.

Now this has some interesting implications.  One of the problems
with teleportation devices in Science Fiction stories is that
they allow for the creation of duplicates.  They reduce an object
to a pattern by measuring it, and then recreate it at a distance
by assembling atoms of the same types according to the
appropriate directions.  There is no theoretical reason why, once
the pattern has been saved, this process could not be repeated
multiple times.  This has implications for things like souls and
self-awareness that many people would rather not think about.

The preceeding method for teleporting mixed quantum states does
not have such a problem, since only things which have not been
measured can be transferred in such a way, and the duplicate can
only be created if the original has been destroyed.  If
consciousness is truly a phenomena involving quantum mechanical
superposition, then we need never worry about being replicated,
and the "transporter accidents" of Star Trek are forever
relagated to the realm of fiction.

In any case, it should be noted that this method works at present
only with single particles, and not with large aggregate systems
like Goulash.  Extending it to systems would appear to be an
intractable engineering problem given current technology.

Those wishing to read IBM's explanation of this new technology
may browse their Web page on Quantum Teleportation at...

  http://www.research.ibm.com/quantuminfo/teleportation/

--
     Mike Duvos         $    PGP 2.6 Public Key available     $
     mpd@netcom.com     $    via Finger.                      $