Efficient single-photon frequency conversion using a Sagnac interferometer

We present a quantum nanophotonic scheme to achieve efficient single-photon frequency conversion. This mechanism is essential for integrated nanophotonics, as it can provide access to frequency regimes in which no single-photon sources are currently available. Moreover, such a device could be used as the basis of a photonic frequency-shift-keyed quantum information scheme. The proposed scheme uses a Sagnac interferometer to exploit quantum interference between two transition pathways in a three-level quantum dot. In the proposed scheme, an input photon induces a complete population state transfer on the Lambda-type quantum dot, causing a frequency shift in the outgoing photon. The Sagnac interferometer is used to put the input photon into a superposition of counterpropagating states which interfere at the quantum dot, providing the necessary quantum interference to make the process efficient. We have developed a real-space theoretical approach and a computationally efficient pseudospectral numerical method to invegtigate the full spatiotemporal dynamics of the scattering process. It is shown that the efficiency of the frequency-conversion process approaches unity in the ideal case, and is greater than 80% even in the presence of realistic dissipation.