A function oracle supplies access to an unknown function : given an allowed input , one query returns . Query complexity counts these accesses separately from known local computation. A classical query receives one definite answer; a quantum oracle specifies coherent access through a unitary operator, allowing inputs in quantum superposition. The distinction is part of the access model, not a change to the mathematical function.
A Boolean quantum oracle preserves and adds a one-bit value into an answer qubit by exclusive or. On known computational-basis states, its output determines the same value as a classical function oracle query.
New to topics? Read the docs here!