Designing stoichiometric Eu³⁺ compounds for dense, optically addressable quantum memory
Quantum memory built with stoichiometric rare-earth materials opposes conventional doped systems. Rather than containing ppm levels of weakly emitting, randomly distributed rare-earth dopants, stoichiometric compounds drastically increase concentrations while improving homogeneity. This, in theory, produces optical spectra with narrow inhomogeneous linewidths that can resolve hyperfine splits with hours-long coherence times, creating high densities of optically addressable rare-earth qubits. The only candidate previously explored, though, has impractical environmental stability issues, unknown defect chemistry, and isotopic purification requirements. To explore how chemical factors influence stoichiometric materials’ linewidth, we first studied known compounds with large Eu³⁺ separation to avoid undesirable cation interactions. We grew metal-organic framework crystals with long optical lifetimes, tracking chemical stability with photoluminescence and X-ray diffraction. Using two flux systems, we also grew an oxide with coexisting polymorphs that shift the Eu³⁺ site symmetry. Still, we wanted to expand the limited list of compounds with large Eu³⁺ separation while also eliminating the need for isotopic purification to reduce linewidths, so we used density functional theory to predict new compounds containing Eu³⁺ and mononuclidic elements. At least two predicted compounds are synthesizable, including a fluoride for which we have characterized the fundamental optical and magnetic properties. Ongoing work entails the optimization of crystal growth conditions and subsequent studies correlating crystal quality with inhomogeneous linewidth.
Student Information: Zach is a fifth-year PhD student in Daniel Shoemaker’s lab in the Materials Science department who works on Eu3+ compounds for quantum memory applications and on antiferromagnets with unexplored magnetic structures.