Interfacing Superconducting Qubits and Telecom Photons via a Rare-Earth   Doped Crystal
  We propose a scheme to couple short single photon pulses to superconducting qubits. An optical photon is first absorbed into an inhomogeneously broadened rare-earth doped crystal using controlled reversible inhomogeneous broadening. The optical excitation is then mapped into a spin state using a series of $\pi$-pulses and subsequently transferred to a superconducting qubit via a microwave cavity. To overcome the intrinsic and engineered inhomogeneous broadening of the optical and spin transitions in rare earth doped crystals, we make use of a special transfer protocol using staggered $\pi$-pulses. We predict total transfer efficiencies on the order of 90%. 
Christopher O'Brien, Nikolai Lauk, Susanne Blum, Giovanna Morigi,   Michael Fleischhauer
quant-ph