When we measure this qubit in the standard basis, the probability of outcome | 0 ⟩ {\displaystyle |0\rangle } is | α | 2 {\displaystyle |\alpha |^{2}} and the probability of outcome | 1 ⟩ {\displaystyle |1\rangle } is | β | 2 {\displaystyle |\beta |^{2}} . Because the absolute squares of the amplitudes equate to probabilities, it follows that α {\displaystyle \alpha } and β {\displaystyle \beta } must be constrained by the equation