Quantum computing FAQ

Last updated: 2002-02-25

Here is some stuff that's tangentially related to Quantum Computing. Just something I (David Cary) threw together that I thought you might find interesting. If you find any more related resources, I would appreciate you telling me about them so I can add (links to) them to this page. Comments?


[FIXME: indicate which links are introductory material, and which ones assume you already know all that stuff.]

David also maintains related files:

quantum computers

tutorials, kinds of quantum computers, general reviews of multiple kinds of quantum computers.

Some related Usenet Newsgroups:

QCA: quantum-dot cellular automata

other quantum computers


[FIXME: move other photonics references here]

I suspect there is a time period where most computation is photonic ... a narrow time wedged between CMOS electronics and early nanotech.

See also machine_vision.html

DNA computing

[FIXME: ...]


other future computing schemes

"rod logic": Drexler described mechanical computing systems in _Nanotechnology_.

http://www.thehub.com.au/~mitch/computing.html (future computing)

``Brainy Bacteria'' article by Dolly Setton, Best of The Web, 09.10.01 http://www.forbes.com/best/2001/0910/016.html

`` One appeal of bacterial computing is that bacteria are very cheap to manufacture. Scientists can grow trillions of bacteria in a lab for a few dollars in material costs. ... It's an appealing prospect, given how expensive computing is today. It costs about $2 billion to build a new semiconductor fabrication plant, where people in space suits work with robots to build the chips that go into personal computers. ''

[FIXME: bignums#money]

"chaos-based computing" http://www.gtri.gatech.edu/res-news/DYNAMIC.html

What is a Computer? ftp://ftp.ans.net/pub/misc/jta/biocompflow.txt by John-Thones Amenyo <jta at ans.net> Copyright 1995, J. Amenyo Lots of various computing possibilities (optical computer, fluidic computer, biocomputers, quantum computers, etc.)

"Plasma waves" http://www.rpi.edu/dept/NewsComm/Review/sept97/sept_12/waves.html

random tangential stuff

An introduction to Quantum Computing, why it's nifty, quantum error correcting codes, etc. http://www.lucifer.com/~sean/BT/14.html#ClarkQuantum

It's possible that one application of quantum computing will be towards Computed Holography.

The Quantum Optics and Atom Optics links page http://www.physics.mq.edu.au/~drice/quoptics.html

Date: Mon, 2 Dec 1996 00:18:02 -0500
From: Michael Frank <mpf at ai.mit.edu>
To: David Cary
Subject: Re: quantum computing links
X-URL: http://www.ai.mit.edu/~mpf

David Cary writes:
 > Would you mind me adding a link to your page on my quantum computing page ?

Sure, no problem.

 > You have some nice content on your web pages. Perhaps you would be
 > interested in the quantum computing page on my web page.

Thanks, your page looks nice.

Interesting to see people discussing the relevance of quantum
computers to public-key cryptography.  In my view, this is still very
much up in the air, even if good quantum computers could be built,
because computer scientists know of plenty of other, equally secure
public-key cryptography schemes that have nothing whatsoever to do
with factoring.  The only reason RSA is so popular is that it was
first.  But if factoring fell, one of the other cryptosystems could
just rise up and take its place.

Of course, it's possible quantum computers would be able to solve
those other public-key cryptosystems as well, but that would have to
be demonstrated.  But anyway, there would still be a big short-term
impact while people switch their software over from RSA to the other
non-factoring-related public-key cryptosystems.


 > p.s.:
 > On your page http://www.ai.mit.edu/~mpf/qclinks.html, you have
 > --
 >  ADD_DATE="818813634" LAST_VISIT="818821896">Q-gol Quantum Programming
 > Language
 > --
 > which has moved.
 > David Cary <*> O-
 > Future Technology.

quantum physics

"Everyone has some intuition about baseball and billiard balls [which is invaluable for engineering mechanical devices. ...] But very few people have intuition about these quantum-mechanical interference and information effects. And the only way to make anything useful with them is if we really do have that good intuition." -- Los Alamos National Laboratory physicist Paul Kwait, quoted in _Science_ 1996 Oct 25 p. 505 article "To Send Data, Physicists Resort to Quantum Voodoo".



interesting speculation on combining quantum computers with neural networks

Date: Fri, 31 Jan 1997 09:38:36 +0100 (MET)
From: Anders Sandberg <nv91-asa at nada.kth.se>
To: transhuman at logrus.org
Subject: Re: >H Transhumanistic Companies/organizations/groups/individuals/etc.
X-MIME-Autoconverted: from 8bit to quoted-printable by siddhartha.us.itd.umich.edu id DAA12815

Transhuman Mailing List

On Fri, 31 Jan 1997, JosŽ S‡ez wrote:

> > Uploading: there is plenty of research going on about simulating realistic
> > biological neurons.
> How do you do that? I want DETAILS.

Some more details (but still incomplete):

Most work have been done in simulating the electrodynamics of the membrane
and synapses by using models for the ion channels and their interactions.
Usually one divids a simulated neuron into cylindrical or spherical
compartments (asumed to be isopotential) with membrane properties set by
the concentrations of different ion channels. Then the membrane
polarization and state is calculated by solving differential equations
(based on the Hodgson-Huxley equations) where each compartment influences
the neighboring compartments (essentially everything can be seen as a
electronic network). Several such model neurons are connected by synapses,
and one studies the output or behavior of the network. Of course, the big
problem is (a) making a good membrane model, and (b) doing the number
crunching (we are happy here at the Institute that we got several paralell

See for example the pages of the SANS group here at Nada
(http://www.nada.kth.se/sans I think) for more discussion. There are links
from there into the wide world of neural networks (although most people
deal with artificial NNs).

[A small aside: the quantum computer discussions gave me a fun idea,
quantum neural networks. It seems that you can train a quantum backprop
net in just one iteration if you can feed it a superposition of all
training patterns and compare the output with a superposition of all
desired output... I think.]

> Since nobody said anything about Si based proteins I assume they don't
> exist as I suspected (Never liked the idea anyway).

I don't think they do. Silicon tends to form weaker bonds than carbon, so
it is possible that you can't make the peptide backbone stable.

Anders Sandberg                                      Towards Ascension!
GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y


quantum computer http://www.nytimes.com/library/national/042898quantum.html

"John Preskill has a beautiful set of [quantum computing] lecture notes available" http://www.theory.caltech.edu/people/preskill/ph229/

Quantum Computers http://qso.lanl.gov/~gottesma/QComputers.html

Date: Tue, 24 Feb 1998 21:23:12 +1000 (EST)
From: Mitchell Porter 
To: transhuman at maniac.deathstar.org
Subject: >H re: Topics of current personal interest
Reply-To: transhuman at logrus.org

Transhuman Mailing List

(I get the digest, so I'm seeing this weeks afterwards.)

David Cary said

> >2. Developing useful applications of NT.
> ...
> >so
> >that we're ready to use the technology the moment it
> >arrives.
> Good point. The most practical plan I've seen so far is to make better golf
> clubs (!) as part of the early bootstrap process.

I don't remember that one! Where'd you see that?

> >5. Conceptualizing and planning for "infinite futures".
> >For example:
> >
> >One can imagine a very fast computer connected to
> >sensors and effectors throughout a baby universe.
> >The computer maintains a model of the state of the rest
> >of the universe, constantly updated via the sensors.
> >There is always a particular finite range of actions
> >open to it through the effectors. What it does is to
> >model the effects of each possible action, some degree
> >into the future, and selects an action on the basis of
> >some criterion ('value system'?) applied to the various
> >projected outcomes.
> How is this different from what sentients do already ?

The difference would be one of degree. I'm talking about
a situation in which the baby universe is saturated with
sensors, in which its model is constantly updated in
realtime, and in which simulations of its future can run
faster than the real thing. So it's a situation of
effective automated omnipotence (if you throw in some
actuators as well, that is).

I'm curious about the logistics of such situations
(e.g. under varying cosmic scenarios: finite versus
infinite universe; baby universes are possible vs
black holes are just massive elementary particles and
don't "lead" anywhere), whether such a future is likely
or necessary, how unreliability of the supervising
system or unpredictable future changes in the intentions
of its programmers might affect the picture, whether
we have any values which lead us to find such a future
inherently undesirable, and so on.

> >10. Quantum compiler. We need a way to turn programs
> >into something that can be run on a quantum computer.
> Should we work on this before or after building quantum computers capable
> of running these programs ?

Thinking about it now should be useful, but first you have to catch
up with the state of quantum computational theory, and then
you have to make it make sense. I'm told that just about every
reasonable position regarding the relative powers of classical
and quantum computers has its proponents, for example. See
for one "manifesto".

Q-gol, at http://rosebay.matra.com.au/~gregb/q-gol//index.html,
is supposed to be a quantum-computing programming language, but
I can't connect to that page any more. A web search on "quantum
compiler" turns up http://www.darpa.mil/ito/Summaries97/F361_0.html,
which lists a string of goals including development of a
quantum compiler and of a desktop quantum computer. That page is
about NMR quantum computing, which is really classically-parallel
bulk quantum computation, in which an Avogadro's number of
molecules are used as individual quantum computers, and NMR is
used to apply the quantum logic gates and to read out the final
state. I'm intrigued by the notion of solid-state NMR quantum
computing. NMRQC has the advantage that the output of a quantum
computer is generally probabilistic (e.g. Shor's algorithm) and
here you're automatically averaging over the output of a zillion
quantum computers running the same program. But all those
molecules are tumbling around and drifting about and undergoing
thermal interaction - surely it would be advantageous to have
your "single-molecule quantum computer" in a vacuum and fixed
in space. So I imagine using advanced nanotech to construct
some rigid, perfectly periodic structure containing
ultra-high-vacuum spaces in which identical copies of the SMQC

> ...
> >12. What it's like to be 'auto-omniscient' (knowing
> >everything about oneself) and 'autopotent' (having
> >the capacity to change any aspect of oneself - term
> >due to Nick Bostrom).
> Deep questions.
> I believe A. Sandberg claimed that the free will is caused by *lack* of
> knowledge about oneself.

'Free will' is one of those terms that *has* to be defined before
you can hope to converse with any mutual understanding. I've heard
people say that one is free insofar as one's behavior is brought
about by one's conscious knowledge and desires (and not external
or unconscious influences), in which case freedom is increased by

[FIXME: #free-will]

Quantum Computing: QUIC Theory at Caltech http://www.theory.caltech.edu/~alandahl/quic.html [offline ?]

"Analog computer trumps Turing model" By Sunny Bains http://www.eetimes.com/story/OEG19981103S0017 "Recent developments ... suggest that analog computations are more powerful than digital ones."

RSFQ Laboratory http://pavel.physics.sunysb.edu/RSFQ/ "RSFQ stands for Rapid Single Flux Quantum logic/memory family. This is an emerging superconductor technology that promises digital data processing at clock frequencies of up to 600GHz with negligible power consumption of ~0.4uW per Josephson junction." Apparently researchers here have already attempted to build a complete general-purpose RSFQ microprocessor. Special software here.

Introduction to Nonlinear and Chaotic Phenomena http://trixie.eecs.berkeley.edu/~chaiwah/introduction.html (Chua's Circuit)


Started: 1995 ?, before 1995 Sep 2

Send comments, suggestions, bug reports to

David Cary

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