Entangling remote quantum repeater nodes

The distribution of entanglement between the nodes of a quantum network will allow new advances e.g. in long distance quantum communication, distributed quantum computing and quantum sensing. On the ground, quantum information can be distributed across the nodes using single photons at telecommunication wavelengths traveling in optical fibers. To bridge distances much longer than the fiber attenuation length, quantum repeaters can be used. The nodes of a quantum repeater are matter systems that should efficiently interact with quantum light, allow entanglement with photons (ideally at telecommunication wavelengths) and serve as a quantum memory allowing long-lived and faithful storage of (entangled) quantum bits. In addition, for efficient distribution of entanglement, the nodes should allow multiplexed operation and ideally enable quantum processing capabilities between stored qubits.

In this talk, after introducing the context I will describe our recent progress towards the realization of quantum repeater nodes with multiplexed ensemble-based quantum memories, using cryogenically cooled rare-earth ion doped solids. I will show how solid-state quantum memories can be entangled with telecom photons using non-degenerate photon pair sources.  I will also describe our efforts to scale up quantum repeater links. In particular, I will report a recent experiment demonstrating entanglement between remote multiplexed solid-state quantum memories, heralded by a telecom photon. Finally, I will explain our current work to build quantum processing nodes using e.g. single rare-earth ions in microcavities or ensembles of cold Rydberg atoms.