Re: Science News - article on Quantum Crypto

[Alexandra Griffin <acg@mandrake.cen.ufl.edu>]

Bob writes:

> Does anyone know if the new in-line optical amplifiers (not switches!) have
> any effect on quantum crypto messages?

Yes, any active devices in your communications path would be unable to
function without making some kind of classical measurement on the
photons involved (e.g. measuring phase relative to a definite test
angle, if phase is what's being modulated), thereby collapsing the
wavefunction and spoiling any special properties afforded by being
able to send photons down the line without "looking at them."  Optical
repeaters have to pass your signal through an intermediate electronic
stage anyway, since we have no purely optical valve/transistor
equivalents (bosons don't interact with each other at all).

Can someone think of a reason why this wouldn't necessarily be so?

> Cheers,
> Bob Hettinga

- alex