Harnessing Atoms to Create Superfast Computers

[R. A. Hettinga]

http://www.nytimes.com/2003/03/07/books/07BOOK.html?th=&pagewanted=print&position=top


March 7, 2003 

Harnessing Atoms to Create Superfast Computers 
By IAN FOSTER 


A SHORTCUT THROUGH TIME 
The Path to the Quantum Computer 
By George Johnson. 
Illustrated. 204 pages. Knopf. $24. 

George Johnson's "Shortcut Through Time" addresses one of the most
excruciatingly complex, mysterious and deeply fascinating topics in
modern science, namely quantum computing: the manipulation of quantum
states to perform computations far faster than is possible on any
conventional computer. The book's remarkable achievement is that it
makes this deeply arcane topic accessible and understandable - even, I
think, for the reader unsophisticated in physics or computing. It
opens a door to broader understanding of this important field and sets
a new standard for science writing.

I was originally reluctant to review this book. I am a computer
scientist with a guilty secret: I've never really understood quantum
computing. How could I write a review without revealing my ignorance?

However, as I began the preface, I became intrigued and then
excited. Mr. Johnson, a contributing science writer for The New York
Times, says he wrote the book not to profile the personalities in the
field, but to lead the reader toward a tentative understanding of
quantum computing. To take the reader along as he, the writer, strains
"to grasp an idea with an imprecise metaphor, only to discard it for
another with a tighter fit, closing in on an airy notion from several
directions, triangulating on approximate truth." And: "I want the
reader to feel that we are both on the same side - outsiders seeking a
foothold on the slippery granite face of a new idea."

I was hooked. So much of what passes for science writing nowadays is
really human-interest journalism, focused on the quirks and conflicts
of science's eccentric personalities, and is only incidentally
concerned with science itself. Yet here was someone who proposed to
take a problem at the forefront of science and address it on its own
terms. Perhaps my ignorance was a virtue: I could serve as an
experimental subject, reading the book and reporting on whether I
arrived at the promised land.

Approached from this perspective, the book took on the allure of a
good mystery. Mr. Johnson, like a seasoned crime writer, sets the
scene and then introduces a series of increasingly intriguing
metaphors, each of which unveils another aspect of Q.C., as I'll call
it. As the story unfolds, it becomes clear that Q.C.'s secret could be
revealed at the turn of any page. For me, the initial forays covered
familiar ground. But Mr. Johnson soon entered unfamiliar territory,
exploring the mysteries of superposition and entanglement.

Along the way, we discover that we are dealing not with an obscure and
eccentric academic curiosity, but with a dangerous character. (In
addition to mystery, we have drama!) Q.C., it has been shown in the
last few years, could defeat some of the fundamental codes that secure
many electronic communications. The security of these public key
cryptography mechanisms relies on the fact that on even the fastest
computers, performing a particular computation - factoring, or
breaking into their constituent pieces, large numbers - takes an
unimaginably long time. Yet in 1994 Peter Shor, a mathematician,
showed how Q.C. could do this same operation much faster - in a few
minutes. Q.C. could provide a shortcut through time.

Just why this is possible is at the heart of this concise but dense
book. The particulars depend on the clever manipulations of two
fundamental properties of the quantum world - superposition and
entanglement. Superposition lets a single quantum switch be on and off
at the same time; entanglement allows the state of one quantum switch
to be linked with that of another. Set up just right, a collection of
such quantum switches can, in principle, be used to build a computer
that manipulates many numbers at once - transforming millions of
numbers in one step, or, via mind-numbingly complex manipulations,
factoring the numbers that support our financial and national
security.

Fortunately for those who use codes to maintain secrets, we also learn
that Q.C. does not exist yet, at least not in a useful form. As
Mr. Johnson notes, the world record for building a quantum computer
involves just seven qubits (quantum switches, pronounced like the word
cubits) operating for less than a second. A quantum computer with
several thousand qubits and able to run for hours is not expected
anytime soon. The problems involved in scaling up are complex and hard
to resolve. They relate to the tendency of superposed quantum states
to collapse to a single value - either on or off - when the real world
impinges.

"A Shortcut Through Time" is not all metaphor. It also touches on the
history of this young field, noting a prescient paper by the physicist
Richard P. Feynman, who postulated in 1982 that quantum computing
might be possible. (Also mentioned is the independent work by a less
famous but just as visionary physicist, Paul Benioff, formerly of the
Argonne National Laboratory.) But what makes this book a delight and a
rare gem of science writing is the science itself, and Mr. Johnson's
engagement with that science. He promises that he is not going to
cheat by implying omniscience with his subject), and he does not. The
result is fascinating and tremendously engaging.

After all this, you may be wondering whether I now understand quantum
computing. Well, there are some who argue that quantum physics is so
foreign to human experience that no one can truly understand it, only
manipulate its mathematical rules. Mr. Johnson does not use
mathematics and he skips many details. ("We are operating here on a
need-to-know basis," he states.) But I found that with him at my side,
I could reach that delicate mental state that feels like
understanding. Now this state, like a quantum superposition, may
collapse to ignorance when I try to explain it to someone, but in the
meantime, I feel less guilty.

Ian Foster is a senior scientist at Argonne National Laboratory and a
professor of computer science at the University of Chicago.

-- 
-----------------
R. A. Hettinga <mailto: rah at ibuc.com>
The Internet Bearer Underwriting Corporation <http://www.ibuc.com/>
44 Farquhar Street, Boston, MA 02131 USA
"... however it may deserve respect for its usefulness and antiquity,
[predicting the end of the world] has not been found agreeable to
experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'

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