Nonclassical correlations between a C-band telecom photon and a stored spin-wave

Future ground-based quantum information networks will likely use single photons transmitted through optical fibers to entangle individual network nodes.To extend communication distances and overcome limitations due to photon absorption in fibers, the concept of quantum repeaters has been proposed.For that purpose, it is required to achieve quantum correlations between the material nodes and photons at telecom wavelengths, which can be sent over long distances in optical fibers.Here, we demonstrate nonclassical correlation between a frequency-converted telecom C-band photon and a spin-wave stored in an atomic ensemble quantum memory.The photons emitted from the ensemble and heralding the spin-waves are converted from 780 to 1552 nm by means of an all-solid-state integrated-waveguide nonlinear device.We show ultra-low-noise operation of the device, enabling a high signalto-noise ratio for the converted single photon, leading to a high spin-wave heralding efficiency.The presented work is an enabling step toward the practical entanglement of remote quantum memories and the entanglement of quantum systems operating at different wavelengths.