Intrinsically Quantum Effects of Axion Dark Matter Are Undetectable

Author(s): Yunjia Bao, Dhong Yeon Cheong, Nicholas L. Rodd, Joey Takach, Lian-Tao Wang, and Kevin Zhou Is the usual treatment of axion dark matter as a classical field reliable? We show that the answer is subtle: the axion field could well be in a quantum state that has no complete classical description, but realistic detectors cannot tell the difference. To see this, we solve a fully quantum model o… [Phys. Rev. Lett. 136, 171601] Published Wed Apr 29, 2026