Measurement

Measurement maps a quantum state to a classical result (e.g. 0/1), and typically disturbs the state.

Born rule (informal)

If $|\psi\rangle = \alpha|0\rangle + \beta|1\rangle$ and you measure in the computational basis, then:

• $P(0)=|\alpha|^2$
• $P(1)=|\beta|^2$