Quantum memory for quantum repeaters

The implementation of quantum memory, i.e. a quantum interface between light and matter, is central to advanced applications of quantum information processing and communication [1]. Notably, quantum memories are key ingredients in quantum repeaters [2], which promise extending quantum communication beyond its current distance limit. After a brief review of the working principle of a quantum repeater and the state-of-the-art of experimental investigations into quantum memory, we will present the reversible transfer of photon-photon entanglement into entanglement between a photon and an excitation in a thulium-doped lithium-niobate waveguide cooled to 3K. Our finding constitutes an important step towards quantum repeaters and fully quantum-enabled networks.