From: ddt@lsd.com (David Del Torto)
Date: Tue, 29 Mar 94 15:42:48 PST
To: Cypherpunks List <cypherpunks@toad.com>
Subject: RANDOM>Quantum Randoms?
Message-ID: <199403292343.PAA17515@mail.netcom.com>
MIME-Version: 1.0
Content-Type: text/plain


Yatahey,

Listen, I've been lurking the list for many moons, but will be visiting more regularly again, so please forgive if this has already been discussed. However much I tilt at Life's many windmills, I never for a moment lack interest in Crypto matters, so natcherly I noticed the juicy tidbit below in Sci Am with great interest (what jumped out at me was the part about "'truly' random numbers").  I OCRed it and am posting it to see if any of you saw it and what comments you might have about its implications for the future generation of randoms... not to mention for regular computing.

   dave

******* David Del Torto              <ddt@lsd.com>          *******
******* Level Seven Development      <internaut@eWorld.com> *******
******* "If you don't like your Government, grow your own." *******

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Quantum Computing Creeps Closer to Reality

More than a decade ago a small group of physicists, among them Richard P. Feynman, began wondering whether it would be possible to harness quantum effects for computation. Until recently, such investigations have been highly abstract and mathematical. Now Seth Lloyd, a researcher at Los Alamos National Laboratory, has proposed in Science how a so-called quantum computer might actually be built.   Lloyd points out that in one sense "everything, including conventional computers, and you and me, is quantum mechanical," since all matter obeys the laws of physics. One feature distinguishing quantum computers from conventional ones, Lloyd explains, is the way they store information. Conventional computers use electrical charge or its absence to represent 0's or l's used in the binary language of data storage.   In a quantum machine, information would be represented by the energy levels of individual particles or clusters of particles, which according to quantum mechanics occupy discrete states; the ground, or "dow

n," state could signify a 0 and the excited, "up" state a 1. Lloyd says such computers could be made out of materials with identical, repeating units that behave quantum mechanically, including long organic molecules, or polymers; arrays of quantum dots, which are clusters of atoms with precisely controllable electronic properties; and crystals. "Something as simple as a salt crystal might do," he states.   Input is supplied by pulses of light or radio waves, which would nudge the atoms, molecules or quantum dots into energy levels representing, say, a particular number. More pulses of light would cause the system to carry out a computation and disgorge an answer. Because quantum systems are notoriously susceptible to disruption from external effects, an error-correction program would monitor the progress of a computation and put it back on track when it goes awry.   Such a computer would be much smaller and faster than any current model, Lloyd contends. It could also perform certain tasks beyond the range o

f

 any classical device by exploiting a bizarre quantum effect known as superposition. Under certain precisely controlled conditions, a particle can briefly inhabit a "superposed" energy state that is, in a sense, both down and up. It has a 50-50 probability of "collapsing" into one state or the other.   Computers that can store information in a superposed form, Lloyd suggests, could generate truly random numbers, a task that has proved fiendishly difficult for classical computers. They could thus solve certain problems with a probabilistic element-such as those involving quantum mechanics-more accurately than can conventional machines.   Rolf Landauer of the IBM Thomas J. Watson Research Center, an authority on the limits of computing, has "a number of reservations" regarding Lloyd's scheme. Landauer argues, for example, that Lloyd's error-correction method will destroy the very superposition that he seeks (for reasons related to the fact that mere observation of a quantum system alters it). Yet Lloyd's work 

is still "a step forward," Landauer says. "He's given us something to evaluate in more detail."  -John Horgan

Scientific American, April 1994, Page 18
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