A Shortcut Through Time

The Path to the Quantum Computer

"Sets a new standard for science writing. . . . A delight and a rare gem." -- Ian Foster, New York Times, March 7, 2003 (read the full review)

"Those in the know tell me the next high tech revolution is quantum computing. But concepts like qubits -- bits that are both on and off -- seem too bizarre to believe. How does this weirdness make computers faster, smarter, and better? Johnson, a New York Times science writer, holds your hand and drops step by step down the rabbit hole. Four hours later, you get it. He makes you smart and quantum computing real." -- Kevin Kelly, Wired, February 2003

"One of our most gifted science writers, Johnson is a master at bringing the reader along, giving increasingly better approximations to the truth. The book is lucid, elegant, brief -- and imbued with the excitement of this rapidly evolving field." -- Joseph F. Traub, Scientific American, February 2003 (read the full review)

"A remarkable achievement. [This book] will help to guide the imagination of the reader into a fascinating future - one in which quantum mechanics might play a prominent role in communication and computation." -- Dirk Bouwmeester, Physics World, August 2003. (read the full review)

"Lucid and accessible . . . Johnson does a fine job of telling a story that makes sense both to those who are completely at home in the mathematical theory of the subatomic world and to those whose reaction to the theory is abject terror. . . . A beguiling combination of clarity and enthusiasm." -- Graham Farmelo, New Scientist, March 29, 2003

"Relying on his skills as a science writer for the New York Times, Johnson uses clocks, tops, and waves to explain a Tinkertoy version of quantum computing that quickly gets the reader involved and hungry to learn more. . . . Don't miss Johnson's journey as he tears down technical barriers and brings the quantum fire from the mountain." -- Andrew J. Landahl, Science magazine, June 6, 2003.

"A heroically lucid account . . . [Johnson] should be arrested for violating Heisenberg's uncertainty principle." -- Jim Holt, New York Times Book Review, April 6, 2003 (read the full review)

"There's nothing like quantum weirdness to remind us that this world was not made with us in mind. We are lucky to have a writer like George Johnson to walk us through it. In 'A Shortcut Through Time,' he gives us a clear, funny and very human tour of this impossible science and where it may be taking us next. I read it and I thought, At last, this computes. Terrific book." -- Jonathan Weiner

"New York Times science writer Johnson (Strange Beauty, 1999, etc.) explains why quantum computers are expected to be the next major breakthrough. The author begins by recalling his youthful disappointment when he received a build-it-yourself computer and discovered how simple it was. But that anticlimax revealed a central truth: all digital computers are in essence bundles of on-off switches. The logical destination of the trend toward miniaturization is a computer in which each switch is a single atom. There is more to the quantum computer, however, than mere compactness, as Johnson makes clear in a quick summary of quantum theory. The beauty of the "qubit" (as scientists have dubbed the quantum bit) is that it can be in several superimposed states: not just "on" or "off," but both at once. Thus, the numbers 1 through 1024 can all be represented at once by ten quantum switches. Put into practice, this capability enables a stunning increase in speed, essential for tackling such problems as the factoring of very large numbers, which is a key to modern cryptography. Johnson spends some time examining ways in which the simple switches that are the basis for computers could be built from quantum parts. He doesn't minimize the difficulties of the task. To give just one example, capturing atoms (or molecules, or subatomic particles) and training them to act as switches requires cooling them close to absolute zero, impractical for desktop applications. Nor are the qubits anywhere near as stable as one would like, with a few seconds the best working lifetime so far achieved. Still, the potential of the nascent technology is fascinating, and if successful, its development is likely to be one ofthe most closely watched scientific stories of the new century. A tantalizing glimpse of how the uncertainties of quantum theory may yet be tamed for work of the highest precision." -- Kirkus Reviews

"Johnson has been nominated for several awards for earlier books on physics and physicists (Strange Beauty; Fire in the Mind). Here he sticks mainly to science, providing a quick overview of a cutting-edge union between quantum theory and computing. The book begins by describing a computer as 'just a box with a bunch of switches.' Although today's computer switches are imbedded in circuitry, they can in principle be made of any material, like the early banks of vacuum tubes; Johnson also recalls a tic-tac-toe-playing machine created from Tinkertoys in the 1970s. An ordinary computer switch, binary in nature, registers as either a zero or a one, but if a single atom were harnessed as a switch, its dual nature as both particle and wave means it could be 'superpositioned,' simultaneously zero and one. A series of such switches could handle complex calculations much more swiftly than conventional computers: an entertaining theory, but impractical. Except that a quantum computer's ability to factor large numbers -- determining the smaller numbers by which they are divisible -- would have a critical application in cryptography, with a string of atoms used to create (or break) complex codes. After discussing competing projects that aim to make the theory of quantum computing a reality, the book concludes with ruminations on the implications of the projects' possible success. Using 'a series of increasingly better cartoons' and plain language, Johnson's slim volume is so straightforward that readers without a technical background will have no problem following his chain of thought." -- Publisher's Weekly

The epigraph:

Clarke's First Law: "When a distinguished but elderly scientist states that something is possible he is almost certainly right. When he states that something is impossible, he is very probably wrong."

Clarke's Second Law: "The only way of discovering the limits of the possible is to venture a little way past them into the impossible."

Clarke's Third Law: "Any sufficiently advanced technology is indistinguishable from magic."

-- Profiles of the Future: An Inquiry into the Limits of the Possible by Arthur C. Clarke

Contents

Copyright 2002 by George Johnson. All rights reserved.

Preface. Inside the Black Box

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