FIG. 1. Frequency shift techniques for quantum dots (QDs).

Relatively small shifts are typically achieved by tuning the QD energy levels, through optical fields (i.e., the light shift/AC Stark shift), strain, and electrical fields (DC Stark shift), as depicted on the left side of the image. The depicted ranges are typical results, but some engineered systems have produced significantly larger shifts [25–28]. Several hundred nanometer shifts have been obtained using quantum frequency conversion of the emitted photons in cm-scale ${\text{χ}}^{(2)}$ nonlinear waveguides (right). Here, we implement four-wave mixing Bragg scattering, a ${\text{χ}}^{(3)}$ non-linear process, in compact and power-efficient microring resonators, producing frequency shifts in an intermediate regime (red region) sufficient to cover the inhomogeneous broadening of QDs. Moreover, large spectral shifts can also be obtained through this process (gray area), enabling spectral shifts spanning from intraband to interband conversion (gray arrow).