  Photoelectric detectors cover a wide frequency spectrum spanning from the far
ultraviolet to the infrared light with high sensitivity, large quantum
efficiency and low dark current. The equivalent photoelectric detection of
microwave frequency photons has remained elusive due to inherent differences
between microwave photon energy and the interband transition energies exploited
in standard photoelectric detectors. Here we present the realization of a
near-ideal microwave photon to electron converter at a frequency typical of
circuit quantum electrodynamics. These unique properties are enabled by the use
of a high kinetic inductance disordered superconductor, granular aluminium, to
enhance the light-matter interaction. This experiment constitutes an important
proof of concept regarding low energy microwave photon to electron conversion
unveiling new possibilities such as the detection of single microwave photons
using charge detection. It finds significance in quantum research openning
doors to a wide array of applications, from quantum-enhanced sensing to
exploring the fundamental properties of quantum states.
