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Frequency conversion in silicon in the single photon regime.

Quantum communication networks require single photon frequency converters, whether to shift photons between wavelength channels, to shift photons to the operating wavelength of a quantum memory, or to shift photons of different wavelengths to be of the same wavelength, to enable a quantum interference. Here, we demonstrate frequency conversion of laser pulses attenuated to the single photon regime in an integrated silicon-on-insulator device using four-wave mixing Bragg scattering, with conversion efficiencies of up to 12%, or 32% after correcting for nonlinear loss created by the pump lasers. The frequency shift can be conveniently chosen by tuning of the pump frequencies. We demonstrate that such frequency conversion enables interference between photons at different frequencies.