Abstract: Experimental searches for axion dark matter often treat the axion as a classical field, but the axion can evolve into a quantum state with no classical analogue. I will present a general argument that the intrinsically quantum effects of these states are always strongly suppressed, so that near-future experiments cannot distinguish a quantum axion from a classical ensemble. Conversely, certain signatures of axion dark matter, such as background-dependent forces and g-2 shifts, are traditionally computed with Feynman diagrams, but I will show how they can be computed much more quickly and reliably with classical methods.