Low-Noise Cascaded Frequency Conversion of $637.2$ nm Light to the Telecommunication C-Band in a Single-Waveguide Device

Abstract: Interconnected quantum devices are the building blocks of quantum networks, where state transduction plays a central role. The frequency conversion of photons into the telecommunication C-band is decisive in taking advantage of current low-loss transmission lines. Here, we report the difference frequency conversion of $637.2$ nm fluorescent light from a cluster of NV centers in diamond to tunable wavelengths between $1559.6$ nm and $1565.2$ nm. In order to avoid detrimental noise from spontaneous emissions, we use a two-step conversion device based on a single-pumped periodic poled lithium niobate waveguide. We observed a total external (internal) conversion efficiency of $3.0\pm0.1$ ($20.5\pm0.8$) $\%$ with a noise rate of $2.4\pm0.8$ ($16\pm5$) cps/GHz.