Fun_People Archive
15 Jan
Quantum Teleportation

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From: Peter Langston <psl>
Date: Thu, 15 Jan 98 13:17:21 -0800
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Subject: Quantum Teleportation

Forwarded-by: Nev Dull <nev@bostic.com>
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8. EXPERIMENTAL QUANTUM TELEPORTATION

Quantum teleportation is the transmission and reconstruction over arbitrary
distances of the state of a quantum system, an effect first suggested by
Bennett et al in 1993 (Phys. Rev. Lett. 70:1895).  The achievement of the
effect depends on the phenomenon of entanglement, an essential feature of
quantum mechanics. Entanglement is unique to quantum mechanics, and involves
a relationship (a "superposition of states") between the possible quantum
states of two entities such that when the possible states of one entity
collapse to a single state as a result of suddenly imposed boundary
conditions, a similar and related collapse occurs in the possible states of
the entangled entity no matter where or how far away the entangled entity
is located. Polarization is essentially a condition in which the properties
of photons are direction dependent, a condition that can be achieved by
passing light through appropriate media. Bouwmeester et al (6 authors, Univ.
of Innsbruck, AT) now report an experimental demonstration of quantum
teleportation involving an initial photon carrying a polarization that is
transferred to one of a pair of entangled photons, with the
polarization-acquiring photon an arbitrary distance from the initial one.
The authors suggest quantum teleportation will be a critical ingredient for
quantum computation networks. Dik Bouwmeester <dik.bouwmeester@uibk.ac.at>
(Nature 11 Dec 97)

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Related Background:
REPORT OF FIRST QUANTUM MECHANICAL ENTANGLEMENT OF ATOMS ...

In the past, evidence of quantum mechanical entanglement has been restricted
to elementary particles such as protons, electrons, and photons. Now E.
Hagley et al, using rubidium atoms prepared in circular Rydberg states
(which means the outer electrons of theatom have been excited to very high
energy states and are far from the nucleus in circular orbits), have shown
quantum mechanical entanglement at the level of atoms. What is involved is
that the experimental apparatus produces two entangled atoms, one atom in
a ground state and the other atom in an excited state, physically separated
so that the entanglement is non-local, and when a measurement is made on
one atom, let us say the atom in a ground state, the other atom
instantaneously presents itself in the excited state -- the result of the
second atom wave function collapse thus determined by the result of the
first atom wave function collapse.  There is talk that before long quantum
mechanical entanglement may be demonstrated for molecules and perhaps even
larger entities.  [Phys. Rev. Lett. 79:1 (1997)]

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QUANTUM PHOTON ENTANGLEMENT AT A DISTANCE OF SEVEN MILES

Whether or not the quantum mechanical behavior of elementary particles is
called mysterious depends, more or less, on the attitude one has. If there
is a demand that the behavior of these particles be explainable with the
logistic structure of human language, then some aspects of their behavior
seem mysterious indeed. On the other hand, if there is a willingness to
admit that the logical structure of human language may not at present be
isomorphic with the logical structure of the laws that govern the behavior
of these particles, then it is probably best to put off notions of mysteries
and take the behavior for what it is. This week there was announced to the
popular press, before publication, the results of a twin-photon experiment
in Switzerland. Nicolas Gisin et al (University of Geneva, CH) reported that
a pair of twin photons split and sent along two diverging paths, when
arriving at terminals seven miles apart, exhibit the phenomenon of quantum
"entanglement".  The gist of it is that the detection of one of the photons
effectively causes the collapse of the spectrum of its wave-function
solutions to a single solution, and this collapse instantaneously causes
the collapse of the possible quantum states of the other photon, in this
case seven miles away. The melodramatic notion (purveyed by the press) is
that information has somehow travelled from one photon to the other at a
speed greater than the speed of light, with the result that great canons of
thought are thereby destroyed. But perhaps the more prosaic reality is that
any attempt to describe non-classical events with language based on
classical laws and perceptions cannot succeed.  (New York Times 22 Jul 97)

© 1998 Peter Langston