Collective strong coupling of cold atoms to an all-fiber ring cavity

Large-scale quantum networks could allow a wide variety of applications in quantum computing and simulation. Here we demonstrate the operation of a single node for use in such a network. We employ a ring geometry all-fiber cavity system for cavity quantum electrodynamics with an ensemble of cold atoms. The fiber cavity contains a nanofiber section, which mediates atom–light interactions through an evanescent field. We observe well-resolved vacuum Rabi splitting of the cavity transmission spectrum in the weak driving limit due to collective enhancement of the coupling rate by the ensemble of atoms, and present a simple theoretical model to describe this. In addition, we stabilize the cavity resonant frequency by utilizing the thermal properties of the nanofiber. This work represents an important step toward implementing a large-scale all-fiber quantum network.