Trapped ions coupled to optical cavities can be used to build up quantum interfaces between stationary and flying qubits in a quantum network. Shared entangled states between different network nodes have proven to be an essential resource for various applications of a quantum network, such as distributed quantum computation. At a first quantum network node, we have trapped ions in a linear Paul trap and coupled them to an optical cavity two centimeter in length. We have demonstrated entanglement of a single ion with a single photon, and used this high-fidelity operation to entangle two ions in a heralded fashion [1,2]. However, the speed of these operations is intrinsically limited by the ion-cavity coupling strength, which is predetermined by the length of the optical cavity.
Fiber-based optical cavities have been coupled to single ions and it has been shown that these microscopic cavities allow access to the strong coupling regime .
Operating in this regime would enable quantum communication protocols to be carried out over long distances with enhanced fidelity and efficiency. With this goal, we have designed and constructed a novel ion-cavity system which incorporates a fiber cavity. In my talk, I will introduce basic building blocks of quantum networks based on trapped ions coupled to optical cavities and will present recent results, including simulation and characterization of our fiber-based ion-cavity system.
 A. Stute et al., Nature. 485, 482 (2012)
 B. Casabone et al., Phys. Rev. Lett. 111, 100505 (2013)
 H. Takahashi et al., arXiv:1808.04031 (2018)