Title: Quantum and Classical Effects of Axion Dark Matter

Host: Arthur Platschorre

Abstract: The search for axion dark matter is rapidly expanding, with new experiments deploying quantum sensing techniques to reach unprecedented precision. But does one need to account for the quantum nature of the axion itself? Using concepts developed in quantum optics, I will show that the axion can easily evolve into a quantum state with no classical analogue. But the intrinsically quantum effects of these states are practically undetectable: there always exists a classical ensemble which gives the same detection statistics, up to higher-order corrections in the axion coupling. Thus, the classical field approximation works even when the axion field's state is not classical at all. The same conclusion holds for a variety of other axion effects said to be inherently quantum.