Frequency translation of quantum states of light by four-wave mixing in optical fiber

We consider, experimentally and theoretically, the quantum frequency translation (i.e., noiseless conversion) of quantum states of light (Fig. 1), including single-photon states. This process is useful for allowing quantum optical systems (atoms, ions, cavities, fibers, detectors) operating at different wavelengths to communicate with each other. We recently developed the process of frequency translation in optical fiber through use of the Bragg scattering four-wave mixing process (Fig. 2). The high nonlinearity and the ability to control dispersion in photonic crystal fiber (PCF) enable efficient translation between nearby photon channels within the visible to-near-infrared spectral range, useful in quantum networks. This offers an important advantage compared with frequency translation using second-order nonlinear optical crystals, which limits the translation process to widely separated frequencies only.