Can Eve repeat?

[Ivan Krstic]

On 24 Sep 2003 08:34:57 -0400, Greg Troxel <gdt at ir.bbn.com> wrote:
[snip]
> In Quantum Cryptography, Eve is allowed to not only observe, but also
> transmit (in the quantum world observing modifies state, so the notion
> of read only doesn't make sense).  Also, Eve is typically accorded
> unlimited computational power.
[snip]

The idea that observing modifies state is something to be approached with 
caution. Read-only does make sense in quantum world; implementations of 
early theoretical work by Elitzur and Vaidman achieved roughly 50% success 
on interaction-free measurements. Later work, relying on the quantum Zeno 
effect, raised the success rate significantly: "Preliminary results from 
new experiments at Los Alamos National Laboratory have demonstrated that 
up to 70 percent of measurements could be interaction-free. We soon hope 
to increase that figure to 85 percent."

The quote comes from a article by Kwiat, Weinfurter and Zeilinger 
published in SciAm, November 1996 -- if they were getting success rates 
like these back then, I wonder what the current status is.

The article is well worth a read. There's a copy online at:
http://www.fortunecity.com/emachines/e11/86/seedark.html

Best regards,
Ivan Krstic

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