Towards a microwave single-photon counter for searching axions

The major task of detecting axions or axion-like particles has two challenges. On the one hand, the ultimate sensitivity is required, down to the energy of a single microwave photon of the yoctojoule range. On the other hand, since the detected events are supposed to be rare, the dark count rate of the detector must be extremely low. We show that this trade-off can be approached due to the peculiar switching dynamics of an underdamped Josephson junction in the phase diffusion regime. The detection of a few photons' energy at 10 GHz with dark count time above 10 s and the efficiency close to unity was demonstrated. Further enhancements require a detailed investigation of the junction switching dynamics.

Automated summary

The detection of axions or axion-like particles is a major task that faces the challenges of achieving ultimate sensitivity and low dark count rate. By studying the switching dynamics of an underdamped Josephson junction, this trade-off can be approached, leading to efficient detection of a few photons' energy.