Analysis of single-photon and linear amplifier detectors for microwave cavity dark matter axion searches

We show that at higher frequencies, and thus higher axion masses, single-photon detectors become competitive and ultimately favored, when compared to quantum-limited linear amplifiers, as the detector technology in microwave cavity experimental searches for galactic halo dark matter axions. The cross-over point in this comparison is of order 10 GHz ($\sim 40\ \mu$eV), not far above the frequencies of current searches.