Grover iteration R=1 gives P=1 for N=4, M=1 (perfect 4-item search)

Textbook special case: Grover search over N=4 items with M=1 marked item gives certainty after a single Grover iteration. The rotation angle is θ = arcsin(√(M/N)) = arcsin(1/2) = π/6; after R=1 iterations the success probability is…