What made you (continue to) want to write a book?

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Many people have asked me why I decided to write a book. A better questions is: “When you realized that writing the book was going to be orders of magnitude harder and take much longer than you thought it would, what made you decide to continue writing the book?”

My co-author, Wolfgang Polak, and I recently received a book review of the sort that is the dream of every author. A dream review is, of course, positive. But more importantly, it praises the aspects of the book that were most important to the author – the reasons the author kept going after other books on the subject came out and the author had a more reasonable (but still too optimistic) estimate of the vast amount of  effort it would take to finish it. (The review appeared in Computing Reviews, but is behind a paywall. Excerpts appear on the book’s Amazon and MIT press web pages.)

In our case,  one of the things that kept us going was that we had specific ideas as to how we wanted to cover a number of topics. While we were writing, I worried each time a new book on quantum computation came  out, but then I’d see that the new book didn’t cover these topics or didn’t cover them in the way we had in mind. One of the thrills in reading the review was seeing the reviewer, Constantin Chassapis, recognize and highlight three of the most important of these topics: measurement, entanglement, the relation between the formal structures of  probability theory and quantum mechanics.

Quantum measurement is such old and well traveled territory that it still seems surprising to me that we saw a better, or at least usefully different, way  to develop it. It was a thrill to see that Chassapis thought it “one of the best introductions to the themes and concepts of quantum measurement that I have ever read.” Similarly, after reviewing papers that misunderstood entanglement, we wanted to drive home that “entanglement is not an absolute property of a quantum state, but that it depends on a specific decomposition of the system into subsystems.” Furthermore, it surprises me that the tensor product structure of probability theory is not discussed more often in probability texts and that “the relationship between the formal structures of probability theory and quantum mechanics” is not better known.

Another reason authors keep going is a deep love of the subject and the desire to share their  enjoyment of the subject with others. For this reason, my favorite sentence in the review is “I really devoured the book, rediscovering the joy of my student days.”

The biggest reason we kept going was that we had many supporters who believed in the project. We are particularly grateful to Michael Heaney and Paul McEvoy both of whom believed in the project enough to read drafts of all the chapters, often reading multiple versions of a chapter as we made revisions. Michael also co-organized a reading group that went through the book and gave us comments that enabled us to provide “a gradual and well-conceived escalation of difficulty in the themes it presents.”  Through that group we learned a lot about what did not work in an earlier draft of the book, without which it would never have had “an overall excellent rhythm” or become “an educational masterwork of a subject that is not easy.”

Many, many thanks to all of the people who helped us along the way.

And may all authors have such a perspicacious reviewer!