Giant nonlinear interaction between two optical beams via a quantum dot embedded in a photonic wire

Optical nonlinearities usually occur at large intensities, but discrete transitions allow for giant nonlinearities operating at the single-photon level. Here, the authors demonstrate a two-mode giant nonlinearity with a single semiconductor quantum dot, embedded in a broadband photonic wire antenna. They exploit two detuned optical transitions associated with the exciton-biexciton quantum-dot level scheme. The reflection of one laser beam is controlled by the other beam with a threshold power as low as ten photons per exciton lifetime (1.6 nW). Such a two-color nonlinearity opens up appealing perspectives for the realization of integrated ultralow-power logical gates and optical quantum gates.