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. $