Chapter 7, Deutsch’s Algorithm

1. This circuit is not reversible. When x = y, the output is 01 regardless of whether x and y are both 0 or x and y are both 1. When x y, the output is 10 regardless of which input is 0 and which is 1.
2. The number of correct shots varies quite a lot because the amount of noise isn’t predictable. Also, some quantum computers tend to be less noisy than others. On IBM devices, the number of correct shots out of 100 is typically in the 90s but sometimes in the 80s.
3. The CNOT gate affects both the top and bottom qubits. But when we add an X gate, we add it to the bottom qubit. The top qubit (the qubit that we eventually measure) remains unchanged.
4. This circuit implements the Opposite_of function. The leftmost X gate reverses the roles of inputs 0 and 1 from what they’d be with the Identity function. Then, the rightmost X gate restores the top qubit to its original 0 value or 1 value. That rightmost X gate has no effect on...