Chapter 3: Quantum Circuit Model of Computation

"As we scale towards a million [qubits], I think we've got some fundamental issues in error correction, control, and maybe quantum physics that can rear their heads," he said, adding that even those problems are "solvable."

– Arvind Krishna, IBM chairman and CEO

Figure 3.1 – Scaling of the quantum computer [authors]

There are fundamental differences between classical computing and quantum computing; classical computing is deterministic with 1s and 0s, and quantum is probabilistic with a twist. Quantum computers work with probability amplitudes, which is a postulate of quantum mechanics (see Section 2.2, Postulate 2 – Probability amplitudes). The probabilistic amplitudes of quantum computing behave differently from classical probabilities in that these values can cancel each other out, which is known as destructive interference.

Destructive interference...