Near-ideal Microwave Photon to Electron Conversion in a High Impedance Quantum Circuit

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.