Investigations of Optical Coherence Properties in an Erbium-doped   Silicate Fiber for Quantum State Storage
  We studied optical coherence properties of the 1.53 $\mu$m telecommunication transition in an Er$^{3+}$-doped silicate optical fiber through spectral holeburning and photon echoes. We find decoherence times of up to 3.8 $\mu$s at a magnetic field of 2.2 Tesla and a temperature of 150 mK. A strong magnetic-field dependent optical dephasing was observed and is believed to arise from an interaction between the electronic Er$^{3+}$ spin and the magnetic moment of tunneling modes in the glass. Furthermore, we observed fine-structure in the Erbium holeburning spectrum originating from superhyperfine interaction with $^{27}$Al host nuclei. Our results show that Er$^{3+}$-doped silicate fibers are promising material candidates for quantum state storage. 
Matthias U. Staudt, Sara R. Hastings-Simon, Mikael Afzelius, Didier   Jaccard, Wolfgang Tittel, Nicolas Gisin