Andreev Optoelectronics: Absorption Spectroscopy and Microwave-Optical Transduction

Superconducting weak-link junctions host electron--hole hybridized excitations called Andreev bound states, which have attracted significant interest for novel superconducting qubit designs. Andreev physics is synonymous with the microwave range. However, the maturation of semiconductor-based Josephson junctions opens the door to the characterization and manipulation of Andreev states by light. We present a model for light--Andreev interaction, finding unique new effects: Optical transitions involving an Andreev level can sidestep Pauli exclusion, resulting in a pair of absorption resonances separated by twice the bound state energy. The paired resonances couple nontrivially, namely continuous-wave absorption requires pumping both simultaneously. Moreover, we show how Andreev bound states can accomplish optical--to--microwave transduction, a key ingredient in quantum networking.

Further reading: https://arxiv.org/abs/2512.04176