Rare earth doped crystals for classical and quantum information

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Montana State University - Bozeman, College of Letters & Science


High-quality rare-earth-ion (REI) doped materials are a prerequisite for many applications such as quantum memories, ultra-high-resolution photonic signal processing, and quantum-limited sensing. Realization of practical solid-state photonic technologies critically depends on finding materials that offer necessary combinations of optical and spin-state coherence, spectral multiplexing capacity, transition wavelengths, and many other key properties. To realize these advances, we continue to improve the fundamental understanding and control of physical processes that govern ion-ion, ion-spin, and ion-lattice interactions. Furthermore, exploring the role of material chemistry and fabrication in determining the observed properties is crucial. With these motivations, we study a range of rare-earth-doped optical materials using powders and single crystals to understand and optimize the properties relevant to quantum memory, quantum transduction, photonic signal processing, and optical cooling applications. In addition to producing, measuring, and analysing spectroscopic and coherence properties of promising material systems, we highlight the engineering of lattice defects to manipulate both static and dynamic disorder. This work spans nine different REI doped materials: four single crystals, Tm 3+:Y 3Ga 5O 12, Yb 3+:YVO 4, Er 3+:Y 3Al 5O 12, and Er 3+:Y 2SiO 5, and five crystalline powders, Er 3+:LiNbO 3, Tm 3+:Y 3Al 5O 12, Tb 3+:Y 3Al 5O 12, Yb 3+:YAG, and Eu 3+:CaCO 3. These choices are based on material properties unique to each system, need for investigation, or potential for systematic comparison of fabrication methods and stoichiometry. Spectral hole burning (SHB), optical and spin coherence measurement techniques are sensitive quantitative characterization tools, complementing traditional optical, chemical, and structural analysis. We find that coherence and spin lifetimes are especially sensitive to low levels of strain and defects in the crystal, undetected by other methods. Properties of REI doped materials are found to vary by orders of magnitude depending on the source, synthesis, and implementation of the materials. Even mild mechanical processing producing large variations in spin lifetimes and SHB properties. These variations are attributed to low levels of glass-like dynamics in the crystalline lattice introduced by inhomogeneous strain and chemical defects, which can be reduced or eliminated by annealing or improved fabrication. Overall, these studies reveal that SHB or coherence measurements are needed to identify material dynamics and guide the fabrication process to reach the true fundamental capabilities of REI materials.




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