Wave-like Dark Matter

Wave-like dark matter is a class of hypothetical new fundamental particles, which could make up dark matter (DM) and have mass of less than about 1eV. This light mass gives those particles macroscopic de Broglie wavelengths. The most prominent example for wave-like DM is the QCD axion, which would also explain why the neutron electric dipole moment is vanishingly small and conserves charge-conjugation-parity symmetry astonishingly well. While the axion mass is unknown over orders of magnitude, typical axion masses are around the μeV range, corresponding to ~km de Broglie wavelengths. Detecting wave-like dark matter therefore requires vastly different technology compared to much heavier particle-like dark matter. Wave-like DM searches exploit the weak coupling of the DM field to the standard model. Axions, for example, can convert to photons under a strong magnetic field. This conversion can be resonantly enhanced in a high-Q LC circuit or resonator cavity. In this talk we will review the case for wave-like DM and outline major detection strategies. We discuss progress towards sensitivity to the most promising models. This comprises a range of innovative ideas for a wide range of wave-like DM masses. These include techniques to increase signal, e.g., with novel large volume-efficient resonants inside the world's largest magnet facilities. At the same time, we survey methods to minimize background with cutting-edge quantum sensing and single photon counting.