Hi Friends,
Check this out!!!!!
****
Quote from:
http://www.physorg.com/news/2012-01-quantum-physicists-entanglement-nonlocality.html
"When it comes to space and time, modern physics defies our intuition in
the most dramatic way. Einstein's relativity theory tells us that time
and space are intimately related and that absolute time is an illusion.
Quantum mechanics, however, is at rest, and its predictions are perhaps
even more astonishing than those of relativity.
In a nutshell, quantum theory tells us that two entangled particles
behave as a single physical object, no matter how far apart they are.
If a measurement is performed on one of these particles, the state of
its distant twin is instantaneously modified.
This effect leads to quantum nonlocality
<http://www.physorg.com/tags/nonlocality/>, the fact that the
correlation between results of local measurements performed on these
particles are so strong, that they could not have been obtained from any
pair of classical systems, such as two computers. To cut a long story
short, it is as if quantum particles live outside space-time -- and
experiments confirm this.
Understanding this phenomenon of quantum inseparability, arguably the
most counter-intuitive feature of the theory, represents a major
challenge of modern physics. A key point is that inseparability appears
under various forms in quantum mechanics. Understanding precisely the
relation between these various forms is a long-sought-after goal.
Writing in Physical Review Letters
<http://www.physorg.com/tags/physical+review+letters/>, Dr Tamas Vertesi
from the Hungarian Academy of Sciences and Dr Nicolas Brunner from the
University of Bristol make a significant step forward in this
direction. They show that the weakest form of entanglement
<http://www.physorg.com/tags/entanglement/> -- so-called undistillable
entanglement -- can lead to quantum nonlocal correlations, the strongest
form of inseparability in quantum mechanics
<http://www.physorg.com/tags/quantum+mechanics/>. According to
Professor Pawel Horodecki, a quantum theorist at the Gdansk University
of Technology, "entanglement is almost 'invisible' in such systems,
which makes it very surprising that they can exhibit nonlocality".
The work of Dr Vertesi and Dr Brunner also goes a long way towards
disproving a long-standing conjecture made in 1999 by Professor Asher
Peres, one of the founders of quantum information
<http://www.physorg.com/tags/quantum+information/> science.
Peres argued that quantum states featuring a particular symmetry under
time-reversal -- known as partial transpose -- can never lead to
nonlocality. All research in this area supported Peres' conjecture --
until now. Vertesi and Brunner's work proves, via a simple example,
that the conjecture is false when three (or more) observers are
present. It remains to be seen whether the conjecture could
nevertheless hold true in the case of two observers.
Alongside its contribution to our understanding of the foundations of
quantum theory, this work raises novel questions in quantum information
science <http://www.physorg.com/tags/quantum+information+science/>. In
particular, it will spark a debate on the role that entanglement and
nonlocality play in quantum information processing tasks, such as in
quantum cryptography and computation."
*More information:* 'Quantum nonlocality does not imply entanglement
distillability', by T. Vertesi and N. Brunner in /Physical Review
Letters/ 108, 030403 (2012).
<http://prl.aps.org/abstract/PRL/v108/i3/e030403>
http://arxiv.org/abs/1106.4850
***
Notice the role that multiple observers play in this!
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