# In the context quantum computation, what is the evidence that querying classical oracles in superposition makes sense?

In quantum computation it is often assumed that if $$f$$ denotes some (classical) Boolean circuit $$\{0,1\}^n \rightarrow \{0,1\}$$, then a quantum circuit can have oracle access to $$f$$, that is the quantum algorithm can query in superposition via,

$$\lvert x, y\rangle\ \mapsto\ \lvert x, f(x)\oplus y\rangle$$

What evidence is there that this (i.e. querying in superposition) is indeed a physically reasonable assumption? Given blackbox access to some $$f$$ how would one go about integrating this into a quantum circuit?