Dear Dr. Dyakonov:

Thank you for your reply from Wed, 13 Feb 2002 11:07:25 +0100.

> A 100-electron atom in its ground state remains intact eternally.
> However,  if we would try to maintain this atom in an arbitrary
> superposition of some  of its excited states, this will not work (one
> reason is spontaneous  radiation emission).  It would be even more
> difficult to control the atom's general evolution by external fields.
>
> I find the ideas of quantum computing quite interesting and useful
> from the  theoretical point of view, like the discussion of  the |cat>
> + |dog> superposition, or of the possibility to reverse at a given
> moment the velocities of all atoms, but I think that neither of the
> three is practically possible.
>
> I don't think that anybody can "prove" that quantum computing
> (or reversing the atoms' velocities to become younger) is
> impossible, like there is no theorem stating that I cannot build the
> |cat> + |dog> superposition, or of teach my cat (or dog) quantum
> electrodynamics.  However, all our past experience in physics
> indicates that any large enough system with continuous degrees of
> freedom can be controlled only on a macroscopic, not microscopic,
> level.
>
> This task of controlling a large system on a microscopic level is not
> specific for quantum mechanics, one can try to accomplish this for
> classical objects too.  It is strange that some people think that the
> quantum part is somehow simpler.
>
> Is a 100-qubit system with its 2^100 independent amplitudes
> (which can vary continuously!) large enough in this sense?  I think
> so, but since there is no forbidding "theorem", there is always room
> for optimism.

Surely there is always room for optimism, the point is that this optimism depends on what we do *not* know: QM is not a complete theory, since "quantum theory does not explain the occurrence of events. So, quantum theory does not explain the first thing we observe about the world around us" (J. Anandan, gr-qc/9808033).

The so-called collapse of wave function predicts catastrophic events such as "smearing" of localization of physical bodies (the measurement problem: A. Sudbery, quant-ph/0011082 and A. Kent, quant-ph/0202064), total incompatibility with GR (collapse of the energy-momentum tensor, D.V. Ahluwalia, gr-qc/9711075), violation of energy-momentum conservation (P. Pearle, quant-ph/0004067), etc.

Not surprisingly, there is no theorem that would ban quantum computing, but fishing in murky waters can hardly be justified from scientific point of view. It's like trying to develop some new, "ground breaking" technology based on black body radiation, before December 14, 1900. Why not? Nobody had observed some ultraviolet catastrophe, so why bother?

Surely people have the right to do whatever they want,

http://members.aon.at/chakalov/Adami.html

Regards,

Dimi
--
Dimiter G. Chakalov
http://members.aon.at/chakalov
http://members.aon.at/chakalov/dimi.html
 

On Tue, 12 Feb 2002 20:28:31 +0200, "Dimiter G. Chakalov" wrote:
>
> Dear Dr. Dyakonov,
>
> Do you agree with the analogy provided by Dr. Steane? He wrote
> (please see the email attached) that, "because atoms with 100
> electrons don't show such behaviour", it is unlikely that 100-way
> entangled qubits would spontaneously relax.
>
> How would you comment on the physics behind this analogy?
>
>
> Regards,
>
> Dimi Chakalov
 

========
Subject: Re: Is Quantum Computation Possible?
Date: Tue, 12 Feb 2002 19:58:51 +0200
From: "Dimiter G. Chakalov" <dchakalov@surfeu.at>
To: Andrew Steane <a.steane1@physics.ox.ac.uk>
CC: Michel Dyakonov <dyakonov@LPM.univ-montp2.fr>
References: 1

Dear Dr. Steane:

Thank you for your reply from Tue, 12 Feb 2002 17:35:03 -0000.

> > For example, you should be able to say something like "if  A
> > proves to be true, then quantum computing will be *practically*
> > impossible, but  A can never happen, for such and such reasons".
>
> For example: "If qubits spontaneously relax whenever there is a
> 100-way entanglement, then quantum computing will be practically
> impossible, but this is unlikely because atoms with 100  electrons
> don't show such behaviour, and it is hard to see how the laws of
> physics could be changed so as to make this sort of thing happen,
> while preserving all the behaviour we already know about."

Perfect.

Regards,

Dimiter G. Chakalov
http://members.aon.at/chakalov
http://members.aon.at/chakalov/dimi.html
--
I find the idea quite intolerable that an electron exposed to radiation should choose of its own free will, not only its moment to jump off, but also its direction. In that case I would rather be a cobbler, or even an employee in a gaming-house, than a physicist.

A. Einstein, Born-Einstein Letters, 29 April 1924