In this remarkably illustrative and thoroughly accessible look at one of the most intriguing frontiers in science and computers, award-winning New York Times writer George Johnson reveals the fascinating world of quantum computing—the holy grail of super computers where the computing power of single atoms is harnassed to create machines capable of almost unimaginable calcu In this remarkably illustrative and thoroughly accessible look at one of the most intriguing frontiers in science and computers, award-winning New York Times writer George Johnson reveals the fascinating world of quantum computing—the holy grail of super computers where the computing power of single atoms is harnassed to create machines capable of almost unimaginable calculations in the blink of an eye. As computer chips continue to shrink in size, scientists anticipate the end of the road: A computer in which each switch is comprised of a single atom. Such a device would operate under a different set of physical laws: The laws of quantum mechanics. Johnson gently leads the curious outsider through the surprisingly simple ideas needed to understand this dream, discussing the current state of the revolution, and ultimately assessing the awesome power these machines could have to change our world.

# A Shortcut Through Time: The Path to the Quantum Computer

In this remarkably illustrative and thoroughly accessible look at one of the most intriguing frontiers in science and computers, award-winning New York Times writer George Johnson reveals the fascinating world of quantum computing—the holy grail of super computers where the computing power of single atoms is harnassed to create machines capable of almost unimaginable calcu In this remarkably illustrative and thoroughly accessible look at one of the most intriguing frontiers in science and computers, award-winning New York Times writer George Johnson reveals the fascinating world of quantum computing—the holy grail of super computers where the computing power of single atoms is harnassed to create machines capable of almost unimaginable calculations in the blink of an eye. As computer chips continue to shrink in size, scientists anticipate the end of the road: A computer in which each switch is comprised of a single atom. Such a device would operate under a different set of physical laws: The laws of quantum mechanics. Johnson gently leads the curious outsider through the surprisingly simple ideas needed to understand this dream, discussing the current state of the revolution, and ultimately assessing the awesome power these machines could have to change our world.

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5out of 5David–This is a book where phrases like “without worrying about the details” and “details aside” occur frequently, as the reader might be discouraged by the mind-bending complexity of quantum mechanics, such as the practical applications of the ability of individual atoms to spin in opposite directions simultaneously. I waded through these dense (but brief) descriptions and puzzling illustrations, and took away the following useful information: 1. The reduction in size and the increase in power of comp This is a book where phrases like “without worrying about the details” and “details aside” occur frequently, as the reader might be discouraged by the mind-bending complexity of quantum mechanics, such as the practical applications of the ability of individual atoms to spin in opposite directions simultaneously. I waded through these dense (but brief) descriptions and puzzling illustrations, and took away the following useful information: 1. The reduction in size and the increase in power of computers is likely to continue for the foreseeable future, and these changes may even become more dramatic than they have been until now (2011). 2. As a result of #1, ALL encryption as we now know it could be rendered obsolete by new technology. If #2 comes to pass, rendering all previously-encrypted data readable, it is difficult to decide which is the more horrifying scenario: 1. This power of decryption is the monopoly of a few individuals, organizations, or governments; 2. This power of decryption is freely available to everyone. I invite you to leave me a comment stating which you find less horrifying, and why. Review from 6 April 2003 NY Times here.

5out of 5Dennis Littrell–Good read about an exciting possibility One of science writer George Johnson's aims in this book is to explain to a general readership how quantum computers might work. The key word is "might." As it stands now there are no quantum computers at work; and, although there is apparently no theoretically reason they won't be developed in the future, there are a host of practical problems to be solved that suggest they may never be developed. Johnson acknowledges as much when he quotes French physicist Good read about an exciting possibility One of science writer George Johnson's aims in this book is to explain to a general readership how quantum computers might work. The key word is "might." As it stands now there are no quantum computers at work; and, although there is apparently no theoretically reason they won't be developed in the future, there are a host of practical problems to be solved that suggest they may never be developed. Johnson acknowledges as much when he quotes French physicists Serge Haroche and Jean-Michel Raimond as saying that the small scale "hands-on experiments" with a few qubits that are currently being done "are more likely to teach us about the processes that would ultimately make the undertaking fail" than to teach "us how to build a large quantum computer." (p. 169) As I understand it, basically the idea behind quantum compters is that (somehow) individual quanta (atoms, photons, electrons) are able to be in a particular state or not to be in a particular state; that is, either the equivalent of yes or no, but also in an indeterminate state; that is, a state that would signal yes and no at the same time! Somehow (and I hope I am forgiven for not fully appreciating this)--somehow because of this fabled indeterminancy, quanta can be used to compute at a speed that is more than exponentially faster than digital computers. Johnson spends some series ink in trying to show how the atoms can hold and crunch numbers as long as they are not disturbed; that is, not measured in any way (which would bring about the famous "collapse of the wave function"). In this manner a problem that would take a digital computer weeks or months to solve could be solved in a fraction of a second. Problems now actually impossible to solve in any reasonable length of time might become tractable after all. The traveling salesman problem which grows exponentially more complex with the addition of each city, might very well yield to a quantum computer since the computational ability of a quantum computer itself grows exponentially with the addition of more quanta. Wow. One of the reasons there is real money going into trying to develop these seemingly magical machines is that at present all the cryptography used by the military and big corporations relies on the fact that digital machines, no matter how fast, are not able to factor the codes. However, a quantum computer could. Furthermore, as Johnson explains, a quantum computer could also develop cryptography that could not be decoded. So, whoever gets there first--assuming somebody can--will at the very least make a whole lot of money. What I found more interesting than the hope for a quantum computer are some of the insights into the quantum word that Johnson provides incidentally. The biggest stunner for me was his assertion that quantum events can be used to generate random numbers. It may come as a surprise to many people but in the world of classical mechanics there is literally no such thing as a truly random number generator. But because radioactive nuclei decay on a random basis, they can, according to Johnson, be used to generate random numbers. He writes that numbers generated in such a manner are "undeniable random." (p. 91) Apparently this conclusion is a consequence of quantum indeterminacy. In a way, it is a circular conclusion since if we could somehow predict the rate of radioactive decay we would violate indeterminacy. I say "circular" when perhaps I should say "as a matter of faith" because there is no way a stream of numbers derived from radioactive nuclei decay can be proven to be random. Indeed, no string of numbers can, by examination, be proven to be random. If QM is true--and it is massively established--then the numbers are random. Perhaps this idea of randomness is similar to the notion of "nothing" in that it is only defined in a negative way, by which I mean random is the absence of order, and order is in the eye of the beholder. What seems random to human beings may be quite orderly from another point of view. Some of the book is pure fantasy. His discussion of quantum banknotes in Chapter 9 is an example of something that is useful to think about because of the light it sheds on the nature of the quantum world, but any chance that we would actually use quantum banknotes (requiring temperatures near absolute zero!) approaches the null set. (p. 146) Other parts of the book are largely tangential (but interesting nonetheless). For example Johnson's exploration in Chapter10 of "nondeterministic polynomial-time" problems, such as the above mentioned traveling salesman problem, the protein-folding problem and the software verification problem, is very interesting. I was not aware that such problems were linked, but according to Johnson if one is solved, the others would yield as well. The current thinking is that the only hope of solving such intractable problems is a large-scale quantum computer. (p. 164) Johnson is hopeful that such a computer can be developed and bases his hope in part on recalling just how intractable the problems toward the development of the sort of computers we have today seemed in the 1940s in the days of the vacuum-tubed Eniac computer which filled an entire room and had only a small fraction of the computational ability of my desktop. (p. 140) However, whether history will repeat itself and the impediments be overcome remains to be seen. It's exciting to think that they will. --Dennis Littrell, author of “The World Is Not as We Think It Is”

5out of 5Christopher Heckman–An outdated introduction to quantum computing. As a mathematician/computer scientist, a few things bothered me. (1) p. 163: "If NP=P, then perhaps creation would become as easy as verification: it would be equally possible to run the machine backward, to make new compositions that were unmistakably like the artist would do." That last part doesn't require P=NP, though. And David Cope had been doing that for about a decade, when Johnson write his book. (2) p. 167: "Is our mathematics just a shorthan An outdated introduction to quantum computing. As a mathematician/computer scientist, a few things bothered me. (1) p. 163: "If NP=P, then perhaps creation would become as easy as verification: it would be equally possible to run the machine backward, to make new compositions that were unmistakably like the artist would do." That last part doesn't require P=NP, though. And David Cope had been doing that for about a decade, when Johnson write his book. (2) p. 167: "Is our mathematics just a shorthand for approximating the behavior of the physical world?" IOW, is our set of rules a model for the universe? Yes. (3) p. 171: "What if one could devise an algorithm that could examine any Turing machine and its tape and determine whether it would eventually halt?" This is (or should be) an embarrassment for Johnson. The reason is that the proof that there is no algorithm to solve this problem shows how to write a program that the halting algorithm will get wrong, and it's one that can be written in a quantum computer. (Basically: "If the halting 'algorithm' says that I will stop, then I'll actually go into an infinite loop instead." It's a one-liner, and the halting algorithm will give the wrong answer as to whether this program halts.) (4) p. 182: "Even odds (50-50) would be .5 (and the amplitude would be the square root of that: 2.24 or -2.24)." This is a howler and should have been caught. The positive square root of 0.5 is 0.7071..., so he didn't even get the digits right. (I suspect he took the square root of 5 and divided by ten, whereas he should have taken the square root of 50 and divided by ten.) (5) p. 188: "A program that was bugless would be incapable, by definition, of carrying out every single task intended by its designers. Conversely, if it fulfilled all its performance specifications, it would inevitably contain an internal flaw." Um, no. It's easy to write a program that always outputs the number 0, and to show that it works. What Johnson means here is that there is no *general method* to do these things for *an arbitrary program*. Specific cases can be handled; there's a whole research area built around this idea (Verification of Correctness).

4out of 5John Weiler–Boring recount of the author’s introduction to sequential computing followed by his “scratching of the surface” of outdated numerical methods. Don’t waste your time here. Instead, look for a more current work.

5out of 5Gregg–If the proposals of what leading edge thinkers say, the ramifications for quantum computing are profound. Imagine a state of existence in which multiple possibilities can be quantified as though they are factual. If I am to understand the concept of superposition, all possible state are in existence at once. If one were to factor lets say a number such as 1,000,000, all the factors would be arrived at simultaneously. If this ideal is pushed to a logical conclusion, what would one expect if a su If the proposals of what leading edge thinkers say, the ramifications for quantum computing are profound. Imagine a state of existence in which multiple possibilities can be quantified as though they are factual. If I am to understand the concept of superposition, all possible state are in existence at once. If one were to factor lets say a number such as 1,000,000, all the factors would be arrived at simultaneously. If this ideal is pushed to a logical conclusion, what would one expect if a sufficient quantum computer (with enough Q-bit) was ask to find the highest number of pi ? If all possible states are arrived at, then all numbers of pi would also exist at once. How could this be if pi is infinite ? You would need an infinite amount of time to find an answer. With a quantum computer, time is slowed down, because multiple possibilities are explored simultaneously. A time machine you say, sort of, its just that time is being used more efficiently. If the Pi question was put to God, what would "its" answer be, could God find the highest number of Pi, or would God fail ? So must there be some answer ? The book then goes on to describe what Einstein called "spooky action at a distance". When two or more particles come into contact with each other, and they are moved, there remains a connection. When one particle is changed its sister particle is changed in proportion. Somehow information is exchanged instantaneously, or faster than light. Cultivating this phenomenon could revolutionize the communication industry. Then there is quantum memory. The text outlines how information is stored in the position, and oscillations of atoms. Theoretically more information can be stored, than there is information in the entire universe. This interpretation follows the edicts of psychometry, in which matter has the memory of everything that it has been a part of. I believe that through the phenomenon of quantum mechanics, as it relates to computing, it will be possible to use such a system as a host body for consciousness. When a soul/consciousness reincarnates, it uses the brain as a host to express itself in this reality. It is the flexibility of the organization of the brain /matter matrix, that makes this possible. Could a quantum computer manifest such an organization of matter flexibility ? This would be a real life ghost in the machine. The book does not touch on this, but the concepts in it lends credence to the ideal. The freedom for matter to exist in difference states/dimensions is the catalyst. I believe a quantum computer of a significant design, could achieve this within 10 years. What does this imply for Artificial intelligence ? The book does not go into too much detail about current A.I applications. One can conjecture, that when a solution is sought to a problem, a robust quantum computer, even running a current A.I program such as Watson or CYC, would do significantly better that conventional technology. Multiple, if not all solutions to a query are arrived at simultaneously. The material of in the book is a little involved, and a fair amount of the information requires rereading. Over all, when this book came out, it was an excellent choice at covering the mechanics of quantum computing, and the type of problems it could solve.

4out of 5Bill–Going into this book I wasn't entirely sure what to expect. I didn't know much of anything about Quantum computing or quantum physics for that matter and I was concerned that such a thin book might not do the subject justice. It turns out my concerns were misplaced. This book takes a pretty difficult subject and somehow converts into language almost anyone can understand. It was really pretty amazing. I won't claim that I could totally grasp everything it laid out. In fact I just took a leap of f Going into this book I wasn't entirely sure what to expect. I didn't know much of anything about Quantum computing or quantum physics for that matter and I was concerned that such a thin book might not do the subject justice. It turns out my concerns were misplaced. This book takes a pretty difficult subject and somehow converts into language almost anyone can understand. It was really pretty amazing. I won't claim that I could totally grasp everything it laid out. In fact I just took a leap of faith a couple of times and assumed the author wasn't pulling my leg just so I could move forward. Some of this stuff just boggles my mind. I don't know if I'll ever see a working Quantum Computer in my life time but if they actually figure out how to get the technology working it will be amazing and I'll be even more glad I read this book. It is a great introduction to the topic and the author, George Johnson (the NY Times science editor) does a commendable job of making a difficult subject digestable.

5out of 5Upom–I read Johnson's The Ten Most Beautiful Experiments, and was really enamored with Johnson's writing style. I decided to read another title about quantum computing. The book's opening was a strangely enlightening essay on the purpose of popular scientific writing. Though it was a bit off topic, I found it enjoyable. As for the actual book, it was a fairly well-written exposition of the theoretical underpinnings for quantum computers: computers that would be able to use the quantum state to do abs I read Johnson's The Ten Most Beautiful Experiments, and was really enamored with Johnson's writing style. I decided to read another title about quantum computing. The book's opening was a strangely enlightening essay on the purpose of popular scientific writing. Though it was a bit off topic, I found it enjoyable. As for the actual book, it was a fairly well-written exposition of the theoretical underpinnings for quantum computers: computers that would be able to use the quantum state to do absolutely outstanding calculations. Johnson's grasp on the topic s great, though his metaphors are a bit clunky, and aren't terribly easy to grasp. This might simply because of the odd nature of quantum mechanics, but it still was difficult. Nonetheless, he does a fairly good job of discussing the possible technology and its applications. Though we may be a while way from a quantum computer, an exciting world lays if they come to fruition.

4out of 5Peter–A great primer for what quantum computing might be able to do. Although with all of these things, as more research is completed, assumptions from even just a few years ago seem out of date. It would have been nice if there was more discussion about the practical impact of quantum computing beyond "the death of encryption". A great primer for what quantum computing might be able to do. Although with all of these things, as more research is completed, assumptions from even just a few years ago seem out of date. It would have been nice if there was more discussion about the practical impact of quantum computing beyond "the death of encryption".

5out of 5Maurice–I've attempted this book several times and I'm still not convinced that my mind is capable of comprehending the ideas within its pages. We may actually invent a quantum computer before I'm able to finish the book. I've attempted this book several times and I'm still not convinced that my mind is capable of comprehending the ideas within its pages. We may actually invent a quantum computer before I'm able to finish the book.

4out of 5John–cool

4out of 5Charles–I bought this book second hand at the Stanton library book fair last year. Now I am reading it to try and understand what my fellow Toastmaster Dr Peter Rohde is researching!

5out of 5David Steele–Scince journalists shouldnt write books trying to explain science

4out of 5Lena–Great start for beginners just delving into the field of quantum computation.

4out of 5Brendan–Oversimplified, but still useful. Didn't know about the quantum compter -> celluar automata connection. ( Also makes clear how important solving NP = P will { would } be ) Oversimplified, but still useful. Didn't know about the quantum compter -> celluar automata connection. ( Also makes clear how important solving NP = P will { would } be )

4out of 5Charlie–a high-level overview of quantum computing - well done, but a little short on technical content

5out of 5David R.–I still have no idea how this would work.

4out of 5Lazza–Enjoyable but I still don't intuitively grasp quantum computing. Enjoyable but I still don't intuitively grasp quantum computing.

4out of 5Yoko–This review has been hidden because it contains spoilers. To view it, click here. It ended before becoming interesting.

4out of 5Warren–Far too shallow.

5out of 5Zac–a decent, though dated at this point (technology moves quiickly), read. the analogies were clear enough for the layman.

5out of 5Kristýna Obrdlíková–To si musím přečíst eště raz.

4out of 5Matt–LOVED this book. Well written, and easy to understand.

4out of 5Chris Balz–The best science writing I've ever read, explaining one of the most awesome topics ever. The best science writing I've ever read, explaining one of the most awesome topics ever.

5out of 5Praveen–4out of 5Zu–4out of 5Michael Gates–5out of 5W.K. Malone–5out of 5Pola–4out of 5Conrad–5out of 5Joanna–