PHYS: Quantum Teleportation

Max More (
Thu, 11 Dec 1997 00:35:36 -0800

The American Institute of Physics Bulletin of Physics News
Number 350 December 10, 1997 by Phillip F. Schewe and Ben

QUANTUM TELEPORTATION has been experimentally
demonstrated by physicists at the University of Innsbruck (Anton
Zeilinger, 011-43-676-305-8608, anton.zeilinger@; Dik
Bouwmeester, First proposed in
1993 by Charles Bennett of IBM (914-945-3118), quantum
teleportation allow physicists to take a photon (or any other
quantum-scale particle, such as an atom), and transfer its properties
(such as its polarization) to another photon--even if the two photons
are on opposite sides of the galaxy. Note that this scheme
transports the particle's properties to the remote location and not the
particle itself. And as with Star Trek's Captain Kirk, whose body
is destroyed at the teleporter and reconstructed at his destination,
the state of the original photon must be destroyed to create an exact
reconstruction at the other end. In the Innsbruck experiment, the
researchers create a pair of photons A and B that are quantum
mechanically "entangled": the polarization of each photon is in a
fuzzy, undetermined state, yet the two photons have a precisely
defined interrelationship. If one photon is later measured to have,
say, a horizontal polarization, then the other photon must "collapse"
into the complementary state of vertical polarization. In the
experiment, one of the entangled photons A arrives at an optical
device at the exact time as a "message" photon M whose
polarization state is to be teleported. These two photons enter a
device where they become indistinguishable, thus effacing our
knowledge of M's polarization (the equivalent of destroying
Kirk).What the researchers have verified is that by ensuring that
M's polarization is complementary to A's, then B's polarization
would now have to assume the same value as M's. In other words,
although M and B have never been in contact, B has been imprinted
with M's polarization value, across the whole galaxy,
instantaneously. This does not mean that faster-than-light
information transfer has occurred. The people at the sending station
must still convey the fact that teleportation had been successful by
making a phone call or using some other light-speed or
sub-light-speed means of communication. While physicists don't
foresee the possibility of teleporting large-scale objects like humans,
this scheme will have uses in quantum computing and cryptography.
(D. Bouwmeester et al., Nature, 11 Dec 1997; see also