[infowar.de] Re: Physics News Update 765

[hemmerle -! - rumms - uni-mannheim - de]

On 14 Feb 2006, at 11:20, physnews -!
- aip -
 org wrote:

> PHYSICS NEWS UPDATE                                                     	
> The American Institute of Physics Bulletin of Physics News
> Number 765  February14, 2006 by Phillip F. Schewe, Ben Stein, and
> Davide Castelvecchi
>                 	
> ATTACK OF THE TELECLONES: Should quantum cryptographers begin to
> worry?  In contrast with everyday matter, quantum systems such as
> photons cannot  be copied, at least not perfectly, according to the
> "no-cloning theorem."  Nonetheless, imperfect cloning is permitted,
> so long as Heisenberg's Uncertainty Principle remains inviolate.
> According to Heisenberg, measuring the position of a particle
> disturbs it, and limits the accuracy to which its complementary
> property (momentum) can be determined, making it impossible to
> reliably replicate the particle's complete set of properties.
> Now, quantum cloning has been combined with quantum teleportation in
> the first full experimental demonstration of "telecloning" by
> scientists at the University of Tokyo, the Japan Science and
> Technology Agency, and the University of York (contact Sam
> Braunstein, schmuel -!
- cs -
 york -
 ac -
 uk and Akira Furusawa,
> akiraf -!
- ap -
 t -
 u-tokyo -
 ac -
 jp). In ideal teleportation, the original is
> destroyed and its exact properties are transmitted to a second,
> remote particle (Heisenberg does not apply because no definitive
> measurements are made on the original particle).  In telecloning,
> the original is destroyed, and its properties are sent to not one
> but two remote particles, with the original's properties
> reconstructed to a maximum accuracy (fidelity) of less than 100%.
> (Heisenberg limits the ability to make clones as otherwise
> researchers could keep making copies of the original particle and
> learn everything about its state.)
> In their experiment, the researchers didn't just teleclone a single
> particle, but rather an entire beam of laser light. They transmitted
> the beam's electric field, specifically its amplitude and phase (but
> not its polarization) to two nearly identical beams at a remote
> location with 58% accuracy or fidelity (out of a theoretical limit
> of 66%).  This remarkable feature of telecloning stems from the very
> magic of  quantum mechanics: quantum entanglement. Telecloning
> stands apart from local cloning and from teleportation in requiring
> "multipartite" entanglement, a form of entanglement in which
> stricter correlations are required between the quantum particles or
> systems, in this case three beams of light.  (An example of a
> multipartite entanglement is the GHZ state between three particles
> that was featured in Update 414.)
> In addition to representing a new quantum-information tool,
> telecloning may have an exotic application: tapping quantum
> cryptographic channels. Quantum cryptographic protocols are so
> secure that they may discover tapping.  Nonetheless, with
> telecloning, the identity and location of the eavesdropper could be
> guaranteed uncompromised. (Koike et al., Physical Review Letters, 17
> February 2006; for an earlier partial demonstration of telecloning,
> between an original photon and one clone at a remote location and
> another clone local to it, see Zhao et al., Phys Rev Lett, 13 July
> 2005)
...
> 
> ***********
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Mit freundlichen Gruessen

Oliver Benjamin Hemmerle



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Dr. Oliver Benjamin Hemmerle, M.A.
Postfach 120840
68059 Mannheim (Baden)
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