Designing stoichiometric Eu3+ materials for dense, optically addressable quantum memory

Rare-earth elements are well suited for building long-lived quantum memory. Their filled 5s and 5p orbitals shield their 4f-4f orbital optical transitions from external influences, leading to long, millisecond-scale optical transition coherence times. Here, we diverge from typical rare-earth doping approaches by using stoichiometric rare-earth compounds for quantum memory systems. Instead of containing low concentrations of randomly dispersed rare-earth cations, stoichiometric systems drastically increase the rare-earth density while improving homogeneity by reducing local strain and point defects. Improved homogeneity then narrows the inhomogeneous linewidth of the optical transitions. For a stoichiometric Eu3+ compound with an ultra-narrow inhomogeneous linewidth, we can resolve optically addressable transitions between nuclear spin states, which have up to hours-long coherence times. But the only compound reported to have the necessary linewidth, Eu35Cl3·6H2O, has practical limitations. To search for new candidates, I began by looking for known Eu3+ compounds with large distances between Eu3+ cations in the crystal lattice. I grew single crystals of the metal-organic frameworks Eu(HCOO)3·(HCONH2)2 and Eu(HCOO)3 from heated solutions. Both have optical lifetimes >1.4 ms at 1.4 K, but only Eu(HCOO)3 is stable in air. I then improved the Eu(HCOO)3 synthesis procedure, producing transparent, well-faceted crystals at room temperature. The second system from my initial search was the layered oxide EuAl3(BO3)4. Growing EuAl3(BO3)4 crystals from two flux systems, I showed that coherent polymorph domains shift the Eu3+ site symmetry within a single crystal. I also used a flux growth procedure to isolate the material’s C2/c polymorph and helped develop a new procedure for synthesizing polycrystalline EuAl3(BO3)4 in a conventional microwave. To limit linewidth broadening from isotopes, I next proposed unrealized stoichiometric Eu3+ candidates containing mononuclidic ions and used DFT to predict their stability, navigating the computational challenges posed by 4f electrons. I then synthesized the new, DFT-predicted double perovskite Cs2NaEuF6. From my DFT calculations and a search of the Materials Project database, I identified phosphates and iodates as the next chemical spaces to search for narrow linewidth compounds. I synthesized crystals of two iodates, NaEu(IO3)4 and Eu(IO3)3, both of which have a high intensity 5D0→7F0 transition at room temperature. My synthesized candidates span a variety of chemical spaces and are platforms for studying the influence of structural motifs and defect chemistry on the inhomogeneous linewidth, providing a pathway to discovering ultra-narrow linewidth compounds.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Materials Science & Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Riedel, Zachary W.

Contributors dc:contributor

• Shoemaker, Daniel P
• Goldschmidt, Elizabeth A
• Schleife, André
• Shim, Moonsub

• Quantum Memory
• Lanthanides
• Rare-earths
• Crystal Growth
• Materials Design
• Photoluminescence
• Diffraction
• Density Functional Theory

Statement dc:rights

• Copyright 2023 Zachary W. Riedel

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/122107

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F122107