From: Carl Ellison <cme@tis.com>
Date: Thu, 29 Sep 94 08:04:43 PDT
To: doug@OpenMind.com
Subject: Re: Anyone seen the 'quantum cryptanalysis' thread on sci.crypt?
In-Reply-To: <199409290052.RAA20821@comsec.com>
Message-ID: <9409291504.AA02322@tis.com>
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>Date: Wed, 28 Sep 1994 11:21:45 -0700
>From: doug@OpenMind.com (Doug Cutrell)


>I won't argue whether Shor's work will be implemented or not within any
>given time period, but I thought that one of the most important properties
>of it is that once (and if) achieved, the resources required to factor
>increasingly large moduli lengths go up only polynomially, not
>exponentially.

The real roadblock might be that there are limits to how many bits there
can be in a register.  NIST's recent Quantum Computation conference
included discussion of the expected lifetime of a computation (what
fraction of a second the computation would have to complete in before the
internal state space goes incoherent).  The more bits are bound together,
the shorter the lifetime of those bits, according to one result.  However,
the more bits you have the longer the computation has to be.  This suggests
that any given Quantum Computer technology point will lead to a maximum
state size (likely in a small number of bits) for a given application.


Trouble is, I'm not a quantum physicist, so my understanding of this is
superficial.  Any real physicists out there?

 - Carl