title: Ultranarrow Optical Inhomogeneous Linewidth in a Stoichiometric Rare-Earth Crystal.
abstract: We obtain a low optical inhomogeneous linewidth of 25 MHz in the stoichiometric rare-earth crystal EuCl_{3}·6H_{2}O by isotopically purifying the crystal in ^{35}Cl. With this linewidth, an important limit for stoichiometric rare-earth crystals is surpassed: the hyperfine structure of ^{153}Eu is spectrally resolved, allowing the whole population of ^{153}Eu^{3+} ions to be prepared in the same hyperfine state using hole-burning techniques. This material also has a very high optical density, and can have long coherence times when deuterated. This combination of properties offers new prospects for quantum information applications. We consider two of these: quantum memories and quantum many-body studies. We detail the improvements in the performance of current memory protocols possible in these high optical depth crystals, and describe how certain memory protocols, such as off-resonant Raman memories, can be implemented for the first time in a solid-state system. We explain how the strong excitation-induced interactions observed in this material resemble those seen in Rydberg systems, and describe how these interactions can lead to quantum many-body states that could be observed using standard optical spectroscopy techniques.
authors.affiliation: Department of Physics, Montana State University, Bozeman, Montana 59717, USA.|Laser Physics Centre, Research School of Physics and Engineering, The Australian National University, Canberra 0200, Australia.
authors.forename: R L
authors.initials: RL
authors.lastname: Ahlefeldt
authors.affiliation: School of Engineering and Information Technology, University of New South Wales at the Australian Defence Force Academy, Canberra 2600, Australia.
authors.forename: M R
authors.initials: MR
authors.lastname: Hush
authors.affiliation: Centre for Quantum Computation and Communication Technology, Research School of Physics and Engineering, The Australian National University, Canberra 0200, Australia.
authors.forename: M J
authors.initials: MJ
authors.lastname: Sellars