A silicon source of heralded single photons at 2 μm

Mid-infrared integrated quantum photonics is a promising platform for applications in sensing and metrology. However, there are only a few examples of on-chip single-photon sources at these wavelengths. These have limited performances with respect to their C-band counterparts. In this work, we demonstrate a new approach to generate heralded single photons in the mid-infrared on a silicon chip. By using a standard C-band pump, the inter-modal spontaneous four-wave mixing enables the generation of the herald idler at 1259.7 nm and the heralded signal at 2015 nm. The idler photon is easily detected with a common infrared single-photon detector while the signal photon is upconverted to visible before its detection. In this way, we are able to operate a mid-infrared source without the need for mid-infrared detectors and laser sources. By measuring a heralded g⁽²⁾ of 0.23 ± 0.08, we demonstrate the single-photon behavior of the source as well as the feasibility of multi-photon coincidence measurements beyond 2 μm with our setup. The source exhibits a high-intrinsic heralding efficiency of (59 ± 5)%, a maximum coincidence to accidental ratio of 40.4 ± 0.9, and a generation probability of 0.70±0.10W^-2.