Synthesis and Optical Quantum Memory Characterization of α-Eu(IO3)3, β-Eu(IO3)3, and NaEu(IO3)4.

Three phases of stoichiometric europium(III) iodate compounds are probed as candidates for optical quantum memory to determine the impact of reaction conditions on phase formation and to relate crystal structure to their ability to host persistent excited states relevant to quantum memory. Hydrothermal synthesis procedures for growing macroscopic single crystals of rectangular-block α-Eu(IO3)3 (P21/c), yellow hexagonal plate β-Eu(IO3)3 (P21/n), and transparent plate NaEu(IO3)4 (Cc) are presented. The ability to burn narrow and long-lived spectral holes on the 7F0 → 5D0 optical transitions is a necessary condition for implementing optical quantum memory. α-Eu(IO3)3 was determined to be incapable of hole-burning due to the presence of insufficient asymmetry of the europium site, which forbids the required optical transition. β-Eu(IO3)3 was determined to be incapable of storing information due to a lack of observed spectral hole burning, likely due to decoherence caused by the closely packed edge-sharing Eu(III) polyhedra. Analysis of each phase's crystal structure suggests that the Eu-Eu nearest neighbor distance and distortion of europium site symmetry are critical material design parameters for quantum memory applications.