Single-photon frequency conversion by exploiting quantum interference

We present a scheme to achieve efficient single-photon frequency conversion by exploiting quantum interference between different transition pathways for single-photon states. As an example, we discuss the single-photon frequency-conversion process in the configuration wherein a $\ensuremath{\Lambda}$-type (Lambda-type) three-level quantum emitter is coupled to a Sagnac interferometer. It is shown that the efficiency of the frequency conversion approaches unity in the ideal case. A real-space theoretical approach and a pseudospectral numerical method are developed, which facilitate the computation for the full spatiotemporal dynamics of the scattering process.