Ultrahigh-Q on-chip silicon-germanium microresonators for quantum transduction

As an entirely monocrystalline photonics platform, Si_1-xGe_x/Si has exceptionally low losses in both microwave [1] optical [2] and domains, with internal optical quality factors reaching 170M at room temperature. At 4 K, Si_1-xGe_x/Si waveguides still have high quality factors but also a low threshold for bistability and pulsation, which are nonlinear optical effects deriving from the interplay between optically generated free carrier dispersion and thermo-optics. While instabilities deriving from them can be detrimental, they can be mitigated by applying DC electric fields. Together with silicon’s intrinsically high third-order nonlinear optical suscetability, this active control over nonlinearities could lead silicon germanium to applications like electro-optic modulation [3], optical logic, Kerr comb generation, and quantum transduction [4].