🚀 go-pugleaf

In article <BvzrDD.D63@access.digex.com>, jthomas@access.digex.com (Joe Thomas) writes:
> In article <141@lorien.OCF.LLNL.GOV> pearson6@llnl.gov writes:
>>One thing bothers me, though, and I wonder if it bothers anybody else.
>>Explanations of the technique's strength rely heavily on the
>>fact that measurements made on a single photon cannot possibly give
>>a complete knowledge of its original state of polarization.
>>While this basic fact is true, the articles seem not to consider the
>>possibility of "amplifying" the photon into a large number of identically
>>polarized photons, and then making many independent measurements on those
>>duplicate photons, from which the original state of polarization can
>>indeed be deduced with the necessary precision.
> 
> You quite correcly state that photons can be "amplified" or "cloned" 
> in the process of stimulated emission.

Quoting from a paper by Ekert and some others:

"According to quantum theory ..[making a copy of the carrier of information]...
cannot in general be completed. Quantum cloning will give a positive result
leaving the state of the original intact only if the adversary knows in advance
that the carrier of information is in a quantum state picked from a particular
set of orthonormal states."

This would seem to rule out the possibility of eavesdropping by cloning.

I'm no expert on this: perhaps someone out there who is could give the last
word?

-- 
James Annan.
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                [  "The only good Tory is a lavatory"  ]
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