We predict that the threshold detectors based on Al Josephson junctions, with critical currents below 100 nA, exhibiting a phase diffusion regime, can be exploited for the microwave photon detection both at 17 mK and 700 mK. We demonstrate a detection of two- and one-photon energies at 5 GHz with 90% and 15% efficiency and dark count time of about 0.1 s and 0.01 s, respectively. The observed weak temperature dependence of the detector's performance in the sub-kelvin range fully confirms its phase-diffusion mode of operation. On the other hand, these results show that inevitable thermal fluctuations are not the main source of the detector noise. Consequently, there is still a room to optimize the detector's performance. These results are important for axion search experiments in the range of 5-25 GHz (20-100 μeV).
@article{arxiv.2405.04426,
title = {Josephson microwave photon detector operating at 0.7 K},
author = {Dmitry A. Ladeynov and Andrey L. Pankratov and Leonid S. Revin and Anna V. Gordeeva and Alexander V. Chiginev and Sergey A. Razov and Evgeny V. Ilichev},
journal= {arXiv preprint arXiv:2405.04426},
year = {2025}
}