Quantum frequency conversion of memory-compatible single photons from 606 nm to the telecom C-band

The coherent manipulation of the frequency of single photons is an important requirement for future quantum network technologies. It allows, for instance, quantum systems emitting in the visible range to be connected to the telecommunication wavelengths, thus extending the communication distances. Here we report on quantum frequency conversion of memory-compatible narrow-bandwidth photons at 606 nm to the telecom C-band at 1552 nm. The 200 ns long photons, compatible with praseodymium-based solid-state quantum memories, are frequency converted using a single-step difference frequency-generation process in a periodically poled lithium niobate waveguide. We characterize the noise processes involved in the conversion and, by applying strong spectral filtering of the noise, we demonstrate high signal-to-noise ratio conversion at the single-photon level (SNR>100, for a mean input photon number per pulse of 1). We finally observe that a memory-compatible heralded single photon with a bandwidth of 1.8 MHz, obtained from a spontaneous parametric down-conversion pair source, still shows a strong non-classical behavior after conversion. We first demonstrate that correlations between heralding and converted heralded photons stay in the non-classical regime. Moreover, we measure the heralded autocorrelation function of the heralded photon using the converter device as a frequency-domain beam splitter, yielding a value of 0.19±0.07. The presented work represents a step towards the connection of several quantum memory systems emitting narrowband visible photons to the telecommunication wavelengths.