This book had the interesting property of making me think bigger thoughts without making me think about any big thoughts in particular. There is notably no central theme, and large, seemingly inconsequential mathematical tangents, but it was a useful study in watching the author constantly generalize over concepts.

I can't say I enjoyed it, and I can't say I'd recommend it to anyone, but it definitely improved my understanding of computation. There are probably better and faster ways of doing that, but this is what I had to work with. ( )

Quantum computers work with qubits, which can have a value of 0, 1 or both! Thus two qubits can represent four states simultaneously (00, 01, 10, and 11).

Firstly the entangled qubits cannot be in a neither state - what state is that, exactly?! Secondly, I don’t like people saying that a qubit can have a value of 1, or 0, or both - you record the qubit state as 1 or 0 when measured (you never record a state of both), before that, it can be in a superposition of the states 1 and 0, but that’s not the same as saying it is in both states, all you can say is it’s in a superposition of those states and predict what’s the probability you will measure each of them. Having said that, the last sentence correctly quotes the four possible measurable states: two entangled qubits will be in one of four states (as listed) when measured - before that, all we can say is that the entangled qubits are in a superposition of all those four states, and predict the probability any particular one of them will be measured.

Faster. That's it. Not magic. Computing and encryption is a race against the ability to crack it or out-compute it. Quantum theory is fake news anyway- the act of you reading (observing) this comment has changed it, oh and it's both a comment and a photo of ABBA at the same time. It may also just vanish into nothingness, or pop into existence from nothing in another part of the universe. Maybe it did? It's possible. Improbable, but you'll never know.

Why not use the current generation of quantum computers to calculate the probability that next generation's quantum decryption will be successfully countered by quantum encryption? ( )

Finished ½ of this; despite his claim that it progresses more slowly than Road to Reality, it ended up much the same for me!

Primarily about computational complexity theory (P =? NP, etc); secondarily about quantum mechanics viewed as a generalized form of probability calculus and as a strengthener of computation; and tertiarily about other matters surprisingly related to computational complexity, such as the consciousness-related ideas of Penrose, the Doomsday Argument, free will, closed timelike curves, and the accelerating expansion of the universe. While it's all of considerable interest and written in a very jaunty style, there's no hiding the fact that most of it is advanced college-level in difficulty. E.g., a reader who had no interest in conjectures such as "Bounded-error Quantum Polynomial-time (BQP) is the most inclusive complexity class of efficiently computable problems" would want to skip large portions of the book.