This nOde
last updated December 30th, 2006 and
is permanently morphing...
(5 Caban (Earth) / 10 K'ank'in - 57/260 -
12.19.13.16.17)


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IBM and quantum teleportation research.
Teleportation
is the name given by
science
fiction writers to the feat of making an object or person
disintegrate
in one place while a perfect replica appears somewhere else. How this
is
accomplished is usually not explained in detail, but the general idea
seems
to be that the original object is scanned in such a way as to extract
all
the
information
from it, then this information is transmitted to the receiving location
and used to construct the replica, not necessarily from the actual
material
of the original, but perhaps from atoms of the same kinds, arranged in
exactly the same pattern as the original. A teleportation machine would
be like a fax machine, except that it would work on 3-dimensional
objects
as well as documents, it would produce an exact copy rather than an
approximate
facsimile, and it would destroy the original in the
process
of scanning it. A few science fiction writers consider teleporters that
preserve the original, and the plot gets complicated when the original
and teleported versions of the same person meet; but the more common
kind
of teleporter destroys the original, functioning as a super
transportation
device, not as a perfect replicator of souls and bodies.
Two years ago an international group of six
scientists,
including IBM Fellow Charles H. Bennett, confirmed the intuitions of
the
majority of science fiction writers by showing that perfect
teleportation
is indeed possible in principle, but only if the original is destroyed.
Meanwhile, other scientists are planning experiments to demonstrate
teleportation
in microscopic objects, such as single atoms or
photons,
in the next few years. But science fiction fans will be disappointed to
learn that no one expects to be able to teleport people or other
macroscopic
objects in the foreseeable future, for a variety of engineering
reasons,
even though it would not violate any fundamental law to do so. Until
recently,
teleportation was not taken seriously by scientists, because it was
thought
to violate the
uncertainty
principle of
quantum
mechanics, which forbids any measuring or scanning process from
extracting
all the information in an atom or other object. According to the
uncertainty
principle, the more accurately an object is
scanned,
the more it is disturbed by the scanning process, until one reaches a
point
where the object's original state has been completely disrupted, still
without having extracted enough information to make a perfect replica.
This sounds like a solid argument against teleportation: if one cannot
extract enough information from an object to make a perfect copy, it
would
seem that a perfect copy cannot be made. But the six scientists found a
way to make an end-run around this logic, using a celebrated and
paradoxical
feature of quantum mechanics known as the
Einstein-Podolsky-Rosen
effect. In brief, they found a way to scan out part of the information
from an object A, which one wishes to teleport, while causing the
remaining,
unscanned, part of the information to pass, via the
Einstein-Podolsky-Rosen
effect, into another object C which has never been in contact with A.
Later,
by applying to C a treatment depending on the scanned-out information,
it is possible to maneuver C into exactly the same state as A was in
before
it was scanned. A itself is no longer in that state, having been
thoroughly
disrupted by the scanning, so what has been achieved is teleportation,
not replication. The unscanned part of the information is conveyed from
A to C by an intermediary object B, which interacts first with C and
then
with A. What? Can it really be correct to say "first ith C and then
with
A"? Surely, in order to convey something from A to C, the delivery
vehicle
must visit A before C, not the other way around. But there is a subtle,
unscannable kind of information that, unlike any material cargo, and
even
unlike ordinary information, can indeed be delivered in such a backward
fashion. This subtle kind of information, also called
"Einstein-Podolsky-Rosen
(EPR) correlation" or "entanglement", has been at least partly
understood
since the 1930s when it was discussed in a famous paper by Albert
Einstein,
Boris Podolsky, and Nathan Rosen. In the 1960s John Bell showed that a
pair of entangled particles, which were once in contact but later move
too far apart to interact directly, can exhibit individually random
behavior
that is too strongly correlated to be explained by classical
statistics.
Experiments on
photons
and other particles have repeatedly confirmed these correlations,
thereby
providing strong evidence for the validity of quantum mechanics, which
neatly explains them. Another well-known fact about EPR correlations is
that they cannot by themselves deliver a meaningful and controllable
message.
It was thought that their only usefulness was in proving the validity
of
quantum mechanics. But now it is known that, through the phenomenon of
quantum teleportation, they can deliver exactly that part of the
information
in an object which is too delicate to be scanned out and delivered by
conventional
methods. This figure compares conventional facsimile transmission with
quantum teleportation (see above). In conventional facsimile
transmission
the original is scanned, extracting partial information about it, but
remains
more or less intact after the scanning process. The scanned information
is sent to the receiving station, where it is imprinted on some raw
material
(eg paper) to produce an approximate copy of the original. In quantum
teleportation
two objects B and C are first brought into contact and then separated.
Object B is taken to the sending station, while object C is taken to
the
receiving station. At the sending station object B is scanned
together
with the original object A which one wishes to teleport, yielding some
information and totally disrupting the state of A and B. The scanned
information
is sent to the receiving station, where it is used to select one of
several
treatments to be applied to object C, thereby putting C into an exact
replica
of the former state of A. To learn more about quantum teleportation,
see
the following articles:
C.H. Bennett, G.
Brassard,
C. Crepeau, R. Jozsa, A. Peres, and W. Wootters, "Teleporting an
Unknown Quantum State via Dual Classical and EPR Channels", Phys. Rev.
Lett. vol. 70, pp 1895-1899 (1993)
(the original 6-author research article).
Tony Sudbury, "Instant
Teleportation", Nature vol.362, pp 586-587 (1993) (a semipopular
account).
Ivars Peterson, Science
News, April 10, 1993, p. 229. (another semipopular account).
Samuel Braunstein, A
fun talk on teleportation
"the music is different
here, the vibrations are different... not like planet earth... planet
earth sound of guns, anger, frustration... there is no one to talk to
on planet earth to understand... it would affect their vibrations, for
the better of course... equation wise, the first thing to do is
consider
time as officially ended... we'll
work on the other side of time... we'll bring them here through either
isotope, teleportation, transmolecularzation... or better still,
teleport the whole planet here through music..."
-
Sun Ra in the film _Space Is The Place_
(vhs/ntsc)
New Scientist
Teleporting larger objects becomes real possibility
19:00 06 February 02
Anil Ananthaswamy
The
dream
of teleporting atoms and molecules - and maybe even larger objects -
has
become a real possibility for the first time. The advance is thanks to
physicists who have suggested a method that in theory could be used to
"entangle" absolutely any kind of particle.
Quantum
entanglement is the bizarre property that allows two particles to
behave
as one, no matter how far apart they are. If you measure the state of
one
particle, you instantly determine the state of the other. This could
one
day allow us to teleport objects by transferring their properties
instantly
from one place to another.
Until now, physicists have only been able to
entangle
photons, electrons and atoms, using different methods in each case. For
instance, atoms are entangled by forcing them to interact inside an
optical
trap, while
photons
are made to interact with a
crystal.
"These schemes are very specific," says Sougato Bose of the University of Oxford. But Bose and Dipankar Home, of the Bose Institute in Calcutta, have now demonstrated a single mechanism that could be used to entangle any particles, even atoms or large molecules.
Beam splitter
To see how it works, consider the angular
momentum
or "spin" of an electron. To entangle the
spins
of two electrons, you first need to make sure they're identical in all
respects but their spin. Then you shoot the electrons simultaneously
into
a beam splitter.
This device "splits" each electron into a quantum state called a superposition, which gives it an equal probability of travelling down either of two paths. Only when you try to detect the electron do you know which path it took. If you split two electrons simultaneously, both paths could have one electron each (which will happen half of the time) or either path could have both.
Bose and Home show mathematically that whenever one electron is detected in each path, they will be entangled. While a similar effect has been demonstrated before for photons, the photons used were already entangled in another way, even before they reached the beam splitter.
"One of the advances we have made is that these two particles could be from completely independent sources," says Bose.
Massive particles
The technique should work for any objects - atoms, molecules and who knows what else - as long as you can split the beam into a quantum superposition.
Anton Zeilinger, a quantum physicist at the
University
of Vienna in Austria, has already shown that this quantum state is
possible
with
buckyballs
- football-shaped molecules of C60. Although entangling such large
objects
is beyond our technical abilities at the moment, this is the first
technique
that might one day make it possible.
Any scheme that expands the range of particles that can be entangled is important, says Zeilinger. Entangling massive particles would mean they could then be used for quantum cryptography, computing and even teleportation.
"It would be fascinating," he says. "The possibility that you can teleport not just quantum states of photons, but also of more massive particles, that in itself is an interesting goal."
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