Computing with Quantum Cats – John Gribbin ****

A new John Gribbin book is always a delight, and he is at his best when exploring the bizarre possibilities of quantum theory. If you aren’t familiar with his previous books on the subject, the title here might be worrying as it suggests some fiendish bio-electronic device where collections of unwilling cats are wired into a computer, but in fact it’s a follow on from earlier titles In Search of Schrödinger’s Cat and Schrödinger’s Kittens, where the relevance of the cats to the topic has become increasingly strained.

What we have here is an introduction to the wonderful world of quantum computers. Usefully, Gribbin leads us in through conventional computing, with workmanlike short biographies of Turing and von Neumann to help make the route to understanding what is going on in devices we use every day, but of which we have little comprehension, much clearer. It’s good to have a computing history that fully takes into account the British contribution, often sidelined by US work, in part because of the way Churchill unfortunately insisted that most of the UK wartime work be destroyed.

The second section of the book takes us into quantum theory, using Richard Feynman and John Bell as the key biographies, while the third concentrates on quantum computing, leading on the perhaps rather less obviously central character of David Deutsch and taking us through some of the many mechanisms for building a quantum computer that are currently being worked on.

Overall this works very well, and we get a powerful insight into the capabilities of this remarkable technology and the huge challenges that are faced in making it work reliably. To get any idea of how quantum computers work it is necessary to give a good background in quantum theory itself, and this is something that Gribbin can do with one hand tied behind his back. It is indicative of the strange nature of quantum theory that when writing on the subject, I take a very different line on some aspects – notably the many worlds interpretation – and yet both views are currently unassailable. You might even say superposed.

If I have any criticism it is that some areas are brushed over just a little too lightly – this isn’t the book to really get a total low-down on quantum physics as it isn’t its central topic. This means that there are a few places were Gribbin effectively says ‘this happens, but you don’t need to understand it.’ The only specific topic I do think could have been handled better is the very important concept of decoherence, which (unless I missed it) is introduced without ever explaining what it means. Certainly in the first reference to it in the index it is used as if it is obvious what it’s about. Yet in reality it is a subtle concept that is hugely important to the quantum computing business. I really wish there had been a few pages putting this straight.

Overall, without doubt the best book I’ve read to provide the general reader with an introduction to quantum computers, and given their potential importance in the future, that has to make it a brilliant addition to any popular science enthusiast’s shelf.

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Review by Brian Clegg