Electrically induced two-photon transparency in semiconductors

Two-photon emission (TPE) in semiconductors was recently observed, enabling possible realizations of efficient room temperature electrically-driven heralded single-photon sources, entanglement sources, two-photon amplifiers and lasers allowing ultra-short optical pulse generation based on the nonlinearity and the wide bandwidth of two-photon gain. Two-photon lasers (TPL) based on stimulated TPE have unique microscopic quantum properties such as squeezed state operation as well as macroscopic ones including threshold dependence on cavity photon number and bi-stability, while pushing further the modulation speed limit. Semiconductor high charge carrier concentrations, mature fabrication technology and the possibility for electrical control offer many advantages for the implementation of TPLs and two-photon amplifiers. The first step towards realizing of semiconductor two-photon amplifiers or TPLs is to achieve two-photon transparency (TPT) condition, which is reported here for the first time in semiconductors (or any solid state medium).