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Quantum Computing for All? books & arts Quantum computing for all? Quantum Computing Nevertheless, the sophistication of the recent high-profile work on intermediate- for Everyone mathematics is at the level advertised, and scale quantum computation. This is partly is readily digestible by mathematically out of necessity, as contemporary research competent high-school students. requires more sophisticated mathematics The explanatory innovation used by to understand, but is also in line with By Chris Bernhardt Bernhardt is to dispense with imaginary Bernhardt’s focus on well-established ideas. numbers. For a physical theory almost In the final chapter, Bernhardt provides defined by the introduction of imaginary an overview of the potential impact numbers, this is an audacious move. of quantum computation across many MIT PRESS: 2019. However, even by slicing off the imaginary disciplines, including cryptography, big 216PP. £20.00 part of the qubits (bits of quantum data, chemistry, optimization problems and information), we can still understand the theoretical computer science. Again, this ax Planck was awarded the Nobel aspects of quantum physics that enable is kept brief as the author sensibly abstains Prize in Physics 100 years ago for quantum computing: superposition and from making predictions about future Mhis discovery of energy quanta. entanglement. Bernhardt introduces these technological advances. At the time, notions of digital computing concepts in detail using simple linear algebra. Quantum Computing for Everyone is pure were somewhat premature, and it would Both superposition and entanglement exposition. While it seems that Bernhardt take several decades before the foundations rely on the concept of state. In physics, has no central thesis to put forward, of modern computing systems were broadly speaking, the state is a complete the implicit argument is this: to really established. As for quantum computing, that description of a physical system from understand quantum computing you need would have to wait until almost the end of which all other quantities of interest can to understand the mathematical language the 20th century to get going. But over the be derived. For example, if you know the in which it is written. This point makes past 25 years or so, quantum computing position and momentum of a ball at any point the book stand apart from others. It is not scientists have been hard at work figuring during its flight, you can solve for its entire quite a technical textbook and not quite a out how to build a quantum computer — motion, past and future — the position and popular science book, it exists somewhere and figuring out what to do with it. Today, momentum are its state. While this sounds in between — there is probably a quantum we have a much clearer picture of both intuitive, it is important to remember that superposition joke in that. concepts, and commercial systems are this state is, in practice, mathematical in On my bookshelf sits my own book, even starting to appear. Chris Bernhardt’s nature. In quantum physics, the state is also Quantum Computing for Babies, next to the Quantum Computing for Everyone, which stated in mathematical terms. However, canonical textbook on the topic, Quantum provides a basic introduction to the field, unlike the classical states of a ball, when Computation and Quantum Information by could have been written at any time in the the mathematical values representing two Michael Nielsen and Isaac Chuang. One past 25 years, but only now does it feel like different possible states of a quantum system is for infants and the other is for graduate the right time for everyone to read it. are added together, the result is another students. Quantum Computing for Everyone Accounts of quantum computing abound possible state. It is as if these mathematical will fit nicely between the two. in popular science books, magazines and even objects are being stacked together, or As someone who often entertains newspapers. These typically aim to provide an superimposed, and the resulting state is called students interested in quantum computing, introduction to quantum computing for a lay a superposition. When such a superposition the book is, for me, a turning point. My audience, but the result is usually a muddled state is created from quite different states heart sinks when a prospective student mess of bad analogies and fantastical (qubits) of pairs of quantum systems, the excitedly tells me they are interested in claims: objects occupying two places at the result is entanglement. And when one of a the discipline because they read a popular same time, quantum computers capable of pair of entangled qubits is measured, it affects science book that paints quantum physics checking all solutions to a problem at once. the second qubit, even if they are far apart. as an exciting place of parallel universes full Bernhardt intentionally avoids introducing But here lies the problem with high-level of open questions ready for the next young quantum computing in a superficial way. descriptions of quantum phenomena — it hotshot to make their seminal contribution. Instead, he aims to leave the reader with is unclear how they can be useful in Quantum Computing for Everyone is a a competent understanding of quantum aiding quantum computation. And thus, much-needed dose of reality, and an honest computing, and does this assuming that they Bernhardt avoids such intuitive descriptions path for the earnest beginner. ❐ have a minimal technical background. of the phenomena and instead teaches From the outset though, Bernhardt the maths required. Reviewed by Chris Ferrie restricts the audience from “everyone” After a relatively lengthy introduction to Centre for Quantum Sofware and Information, to those “comfortable with high-school classical logic and computation, Bernhardt University of Technology Sydney, Sydney, New South mathematics”. Yes, this book has maths arrives at quantum computing, which is Wales, Australia. in it — and not just a few equations to described at the level of detailed quantum e-mail: [email protected] illustrate a point. It has calculations that algorithms using linear algebra and logic you need to follow in detail — with pen gates. He discusses the standard algorithms Published online: 15 March 2019 and paper — to understand the point. from the mid-1990s, notably leaving out the https://doi.org/10.1038/s41928-019-0223-4 90 NATURE ELecTRONICS | VOL 2 | MARCH 2019 | 90 | www.nature.com/natureelectronics.
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