Quantum repeater node with free-space coupled trapped ions

Quantum repeater cells are crucial for overcoming loss in long-distance quantum networks. Here, the authors present a trapped-ion implementation of a quantum repeater cell, using two ${}^{40}$Ca${}^{+}$ ions that act as quantum memories and are coupled to free-space photonic channels. With this setup they are able to demonstrate asynchronous generation of atom-photon and photon-photon entanglement.