[IP] more on Could freezing light negate Quantum cryptography?

[David Farber <dave@farber.net>]

Begin forwarded message:

From: Vadim Antonov <avg@kotovnik.com>
Date: August 4, 2006 10:36:24 PM EDT
To: David Farber <dave@farber.net>
Cc: ip@v2.listbox.com
Subject: Re: [IP] Could freezing light negate Quantum cryptography?




> Dave,
>
> This month's IEEE Spectrum article : http://www.spectrum.ieee.org/
> aug06/4252
>
> to my very amateur mind raises questions about the viability of
> quantum cryptography.
>
> If a photon can be frozen (and I can't say whether their technique
> can be extended
> to the photon level) can it be measured in its frozen state?  That
> would make the
> difference.
>
> Richard Outerbridge

No, there's so-called "no cloning" theorem, which basically says that
quantum state cannot be cloned.  The act of reading quantum information
destroys it, so it merely shifts to the new place.

The photons are not really frozen - they are absorbed by atoms, and
their state is recorded in the quantum state of atoms.  Then, when
conditions change, they are re-emitted. As particles, photons have no
mass - meaning they cannot move slower than the speed of light.

Regards,

--vadim



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