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update.350 (fwd)
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>From [email protected] Wed Dec 10 16:59:59 1997
Date: Wed, 10 Dec 97 14:35:44 EST
From: [email protected] (AIP listserver)
Message-Id: <[email protected]>
To: [email protected]
Subject: update.350
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 350 December 10, 1997 by Phillip F. Schewe and Ben
Stein
QUANTUM TELEPORTATION has been experimentally
demonstrated by physicists at the University of Innsbruck (Anton
Zeilinger, 011-43-676-305-8608, anton.zeilinger@ uibk.ac.at; Dik
Bouwmeester, [email protected]). 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
www.aip.org/physnews/graphics)
DO EARTHQUAKES HAVE ELECTRICAL PRECURSORS? The
elastic waves measured by seismometers are transmitted by the
flexing crust while an earthquake is doing its worst. But some
scientists believe that flexing also goes on in the hours and even
weeks before a quake. Too small to be detected seismically, the
flexing might well be sensed electrically. As underground strata
rearrange themselves before a quake, the thinking goes, pockets of
water are squeezed into new configurations, changing local
conduction properties, which can be monitored with buried
electrodes. On this basis Panayiotis Varotsos at the University of
Athens (011-30-1-894-9849, [email protected]), has
reportedly predicted certain quakes in Greece weeks ahead of time
by triangulating voltage differentials at the level of 10 millivolts/km
over distances of 100 km. (Some skeptics dispute this assertion.)
In new research, Varotsos buttresses his claims with laboratory
studies of another system under pressure which puts out transient
electrical signals before it fractures, namely a crystal containing a
variety of dislocations and defects. Conductivity patterns in the
crystal convince Varotsos that analogous patterns (although on a
much bigger distance scale) observed in the buried electrode arrays
constitute a true earthquake precursor. (Varotsos et al., Journal of
Applied Physics, 1 Jan, 1998; journalists can obtain the paper from
[email protected].)