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From: rimey@ucbmiro.ARPA (Ken Rimey)
Newsgroups: net.physics
Subject: Re: Smallest possible memory element
Message-ID: <9045@ucbvax.ARPA>
Date: Sat, 13-Jul-85 07:29:11 EDT
Article-I.D.: ucbvax.9045
Posted: Sat Jul 13 07:29:11 1985
Date-Received: Sun, 14-Jul-85 08:26:43 EDT
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Reply-To: rimey@ucbmiro.UUCP (Ken rimey)
Organization: U.C. Berkeley
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>>	Given the technology to do it, the smallest a computer memory
>>could be made would probably be an electron, in that a spin in one
>>direction would be a one and a spin in the other direction would be a 
>>zero.  ...
>>							Eric
>
>   there is a problem here. according to Heisenberg, reading a file
>would irreversibly garble it.
>
>                                          -phil

You say that sensing the spin of an electron would garble it.  I don't
see why.  Is your reference to Heisenberg a reference to the Heisenberg
uncertainty principle?  I don't see how it applies.  It relates to
pairs of simultaneously unknowable observables.  For example, if you
measure the momentum of a particle you disturb its position.  This is
simply because a state of well-defined momentum is a plane-wave, which
clearly does not have a well-defined position.  Excuse me if you already
know this.  Anyway, I don't see that this prevents you from non-destructively
measuring whether a spin is up or down.  Am I missing something?

					Ken Rimey