Optical cavities offer a coherent interface between matter and light, enabling the transfer of quantum information onto photons for long-distance distribution. We demonstrate such an interface by coupling trapped ions to a cavity and have recently shown that a quantum state can be faithfully transferred from an ion onto a photon. Furthermore, this transfer can be improved by taking advantage of a collective effect between multiple ions, namely, superradiant emission into the cavity. By constructing an interface based on entangled ions, one can thus relax the technical requirements for the faithful mapping of quantum information. Finally, prospects for linking together distant ions in cavities via a quantum network will be discussed.