Only one Grover iteration is required. For one marked item among four, the initial marked amplitude corresponds to an angle $\theta$ with $\sin\theta=1/2$, so $\theta=\pi/6$; one iteration changes this to $3\theta=\pi/2$, giving unit success amplitude. Further iterations are neither needed nor beneficial.


Solution

Past exam of the mathematics course of the University of Cambridge / 2025 / ii / Paper 3 / 10C / b / iv / Solution

 Solution (source code)