Microwave single-photon detectors are required in many terrestrial and space applications, like precise measurements of the microwave background radiation and dark matter particle detection (which may deexcite by emitting long wavelength photons). While fluxes of such long wavelength photons may be detected by current technology, detecting them one by one is very difficult because of their low energy—the energy of a typical 1 cm wavelength microwave photon is approximately 0.12 meV or 1.44 kB. Such a small amount of energy should produce a detectable signal in our device, with an adequate repetition rate and with low enough black counts (false signals). Moreover, for astronomical observations, these devices must be sent in space so they should be robust, light, and easy to manipulate.

The race to realize such devices is still on, but we think we have two very good candidates: the cold electron bolometer [1] and the detector based on Josephson junctions [2]. I will show the principles of operation of these devices, focusing on the fundamental physics aspects that had to be clarified to understand their properties and their response.

[1] D. V. Anghel, L. S. Kuzmin, Cold-electron bolometer, as a 1 cm wavelength photon counter, Phys. Rev. Applied 13, 024028 (2020).
[2] D. V. Anghel, K. Kulikov, Y. M. Galperin, and L. S. Kuzmin, Electromagnetic radiation detectors based on Josephson junctions: Effective Hamiltonian, Phys. Rev. B 101, 024511 (2020).