Photon counting for axion interferometry

Axions and axionlike particles are well-motivated dark matter candidates. We propose a novel experiment that uses single-photon detection interferometry to search for axions and axionlike particles in the Galactic halo. We show that photon counting with a dark count rate of 6×10^-6 Hz can improve the quantum sensitivity of axion interferometry by a factor of 50 compared to the quantum-enhanced heterodyne readout for 5-m-long optical resonators. The proposed experimental method has the potential to be scaled up to kilometer-long facilities, enabling the detection or setting of constraints on the axion-photon coupling coefficient of 10^-17-10^-16 GeV^-1 for axion masses ranging from 0.1 to 1 neV.