Coined quantum walk on complete graph — O(√N) quadratic speedup
Coined Quantum Walk Search: Each vertex carries a coin (2-state quantum system). The Grover coin G flips amplitude patterns. An oracle marks the target vertex. After ~π√N/2 steps the probability concentrates on the target — quadratic speedup over classical O(N) search. The separatrix between libration and rotation corresponds to the quantum/classical boundary.