Rare-earth-doped LiNbO3 and KTiOPO4 (KTP) for waveguide quantum memories

Optical waveguides in rare-earth-doped crystals are one of the most promising systems for practical implementations of quantum memory. To further develop these systems, detailed understanding of these materials is required. We report experimental studies of the optical properties and decoherence for Tm3+:LiNbO3, Pr3+:LiNbO3, Er3+:LiNbO3 and Er3+:KTiOPO4 (KTP) bulk crystals for quantum memory applications and discuss potential differences between the properties of the bulk single crystals and optical waveguides. These systems include the rare-earth ions most commonly exploited in quantum memory studies incorporated into two of the most technologically significant waveguide host materials. Photon echo methods were used to study decoherence as a function of temperature, applied magnetic field strength, dopant concentration and excitation wavelength. Decoherence mechanisms were investigated and modelled to interpret the observed behaviour. Spectral hole burning was used to characterize Stark and Zeeman effects. Bulk crystal properties were compared and contrasted to the properties of doped waveguides.