Stoichiometric rare-earth materials at cryogenic temperatures as a platform for quantum memory devices

Rare earth ions in solids at cryogenic temperatures are an excellent platform for developing quantum memory, a device that can store and retrieve single photons on demand. We seek to realize such a device toward the ultimate goal of long-distance quantum communication. Rare earth ions in solids have long-lived optical and spin coherence properties—milliseconds and as long as hours, respectively. Their unique electronic structure affords them these long coherence properties. Additionally, they lack motional dephasing and can have a high density of emitters. The primary challenge we face is the inhomogeneous broadening of the optical transition -- site-to-site variations of the energy levels due to defects in the solid host. The rare earth ions experience different local environments, resulting in a spread of transition frequencies that can be many orders of magnitude broader than the ion’s narrow homogeneous linewidths and the hyperfine spin state splitting. Due to the inhomogeneous broadening, we cannot optically resolve the hyperfine spin states in our ion of choice, Eu3+. The consequence of our inability to resolve the hyperfine states is that we cannot efficiently utilize the hyperfine spin states' long-lived coherence properties for an efficient quantum memory. Rare earth ions are traditionally doped within the host matrix and are themselves defects in the solid. Stoichiometric materials, materials in which the elements appear in proportion to their chemical formula, are a possible avenue toward realizing high-density rare earth materials with ultranarrow inhomogeneous linewidths. Stoichiometric materials are moving to a regime of 100% doping regime where the local environment of the rare earth ions should be more homogeneous. Stoichiometric materials offer an avenue to reduce inhomogeneity, enabling efficient quantum memory with long storage times. Here, I will discuss several materials that we have probed toward the goal of finding an environmentally stable Eu\ion{} material with ultranarrow optical linewidths for a quantum memory device. The first materials we explored were two metal-organic frameworks, EF and EFFA, where we characterized their luminescence properties at room temperature and 1.4 K. The next material we investigated was sodium europium tetrakis(iodate), which exhibits inhomogeneous linewidths as narrow as 2.2(1) GHz and a homogeneous linewidth of 120(10) kHz. Additionally, we have measured the hyperfine spin lifetime to be > 1 s, which sets the ultimate limit on the hyperfine spin coherence time and, thus, the maximum storage time. Finally, we implement a preliminary demonstration of an atomic frequency comb, pushing forward our goal of utilizing sodium europium tetrakis(iodate) as a quantum memory. Preliminary results for other materials I have explored are also included, such as: europium trialuminum borate, europium tris(iodate) and bis(tetramethylammonium) potassium hexakis(nitrato)-europium(III).

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Pearson, Jr., Donny R.

Contributors dc:contributor

• Goldschmidt, Elizabeth A
• Lorenz, Virginia O
• Shoemaker, Daniel P
• Anderson, Chris P

• europium
• stoichiometric materials
• quantum memory
• rare earth ions
• photoluminescence
• optical coherence
• spectroscopy

Statement dc:rights

• Copyright 2025 Donny R. Pearson Jr.

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129371

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129371