Quantum Computing.
functions and ƒ_1 and ƒ_2 are not. Classically we need two evaluations of ƒ(x) to know if ƒ(x) is constant or not. In quantum computing we use an oracle defined using the unknown function ƒ(x) and apply it so U_H (-1)^ƒ(x) U_H|0⟩ = U_H (-1)^ƒ(x) (√2)-1((|0⟩ + |1⟩) If ƒ(x) is constant the oracle