Telecom quantum photonic interface for a 40Ca+ single-ion quantum memory

Abstract Entanglement-based quantum networks require quantum photonic interfaces between stationary quantum memories and photons, enabling entanglement distribution. Here we present such a photonic interface, designed for connecting a 40 Ca + single-ion quantum memory to the telecom C-band. The interface combines a memory-resonant, cavity-enhanced spontaneous parametric down-conversion photon pair source with bi-directional polarization-conserving quantum frequency conversion. We demonstrate preservation of high-fidelity entanglement during conversion, fiber transmission over up to 40 km and back-conversion to the memory wavelength. Even for the longest distance and bi-directional conversion the entanglement fidelity remains larger than 95% (98%) without (with) background correction.