[34] Show that every quantum Turing machine can be simulated to every degree of precision by a quantum Turing machine that has a single primitive rotation θ with cos θ = 3 5 and sin θ = 4 5 .

Comments. Hence, we can restrict ourselves to such quantum Turing machines in the definition of KQ. Then, there are only countably many Turing machines, they can be enumerated, and the universal machine simulates the others exactly. Source: [L.M. Adleman, J. DeMarrais, and M.-D.A. Huang SIAM J. Comput., 26:5(1997), 1524–1540].