The following is a summary of the chapter ‘Quantum Computers’, from David Deutsch’s book, The Fabric of Reality. I recommend reading the original work. Quantum mechanical effects are dominant in all sufficiently small systems. A quantum computer (QC) is a machine that uses uniquely quantum-mechanical effects, especially interference, to perform wholly new types of computation that would be impossible, even in principle, on any Turing machine, and hence on any classical computer. QCs will be t...