Expérimental et théorique
Central to the development of long-distance quantum communications is the concept of quantum repeater. It consists in dividing a long communication channel into various shorter segments over which entanglement can be faithfully distributed. Adjacent segments are then connected by entanglement swapping operations. To be scalable, this approach requires quantum memories, which enable quantum states to be stored at each intermediate node. In this context, the LKB team developed a large cold atomic ensemble based on an elongated magneto-optical trap (3-cm long), enabling 90% efficiency for entanglement storage between two memories. This is the state-of-the-art in term of storage-and-retrieval efficiency for a quantum memory, regardless of the physical platform considered. The work is now focusing on two directions. A first one is to improve other figures of merit, including storage lifetime and multimode capacity. A second one is the demonstration of a 50-km telecom quantum repeater link relying on two distant quantum memories and frequency non-degenerate photon pair sources.