Quantum networks based on nitrogen-vacancy (N-
V) color centers in diamond will enable technology such as communication secured by the laws of nature, and blind quantum computation in the cloud. However, scaling to large distances and many nodes is hindered by the small coherent photon emission and collection from N-
V centers. By embedding a thin diamond membrane bearing coherent color centers into an open, tunable fiber-based optical microcavity, the authors demonstrate that the centers' emission can be enhanced in a fashion compatible with entanglement generation. This work is an important step toward employing N-
V centers in large-scale quantum networks with long coherence.
With the ability to transfer and process quantum information, large-scale quantum networks will enable a suite of fundamentally new applications, from quantum communications to distributed sensing, metrology, and computing. This Perspective reviews requirements for quantum network nodes and color centers in diamond as suitable node candidates. We give a brief overview of state-of-the-art quantum network experiments employing color centers in diamond and discuss future research directions, focusing, in particular, on the control and coherence of qubits that distribute and store entangled states, and on efficient spin–photon interfaces. We discuss a route toward large-scale integrated devices combining color centers in diamond with other photonic materials and give an outlook toward realistic future quantum network protocol implementations and applications.