Efficient Microwave Photon to Electron Conversion in a High Impedance Quantum Circuit

TL;DR

This paper reports a highly efficient microwave photon to electron conversion using a high impedance superconductor, achieving 83% efficiency and enabling detection of individual microwave photons with charge-based methods.

Contribution

It introduces a novel high impedance superconductor to enhance photon-electron conversion efficiency and demonstrates strong coupling effects at low light intensities.

Findings

Quantum efficiency of 83% achieved

Observation of multi-photon to single-electron conversion

Theoretical model matches experimental data

Abstract

We demonstrate an efficient and continuous microwave photon to electron converter with large quantum efficiency ($83\%$) and low dark current. These unique properties are enabled by the use of a high kinetic inductance disordered superconductor, granular aluminium, to enhance light-matter interaction and the coupling of microwave photons to electron tunneling processes. As a consequence of strong coupling, we observe both linear and non-linear photon-assisted processes where 2, 3 and 4 photons are converted into a single electron at unprecedentedly low light intensities. Theoretical predictions, which require quantization of the photonic field within a quantum master equation framework, reproduce well the experimental data. This experimental advancement brings the foundation for high-efficiency detection of individual microwave photons using charge-based detection techniques.