ON QUANTUM TELEPORTATION

 

 

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. Polarizat-

ion 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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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 the atom 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)

 

 

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