LEAPS-MPS: Controllable Disorder as a Path to Many-Body Entanglement in Quantum Magnets

Non-technical Description: Quantum information technologies rely on quantum entanglement, or the intrinsic linking of one quantum object to another. An important research objective is to gain a fundamental understanding of many-body quantum entanglement involving large numbers of quantum objects. Certain magnetic materials known as geometrically frustrated magnets provide a valuable platform for this topic of study because they may exhibit many-body entanglement at low temperature. This project advances the search for promising quantum-entangled frustrated magnets through a systematic investigation of the role of atomic-scale disorder in promoting or hindering many-body entanglement. The results illuminate strategies for utilizing disorder to promote quantum-entangled ground states and contribute to a deeper understanding of many-body quantum entanglement in general. These research activities are integrated into education and outreach efforts including intensive undergraduate mentoring, summer research internships for diverse students, and a new organization called the Physics Breakfast Club that supports regional high-school physics teachers by building community and providing teaching resources. Technical Description: Recent work suggests that disorder in certain types of frustrated magnets can stabilize entangled magnetic states such as a quantum spin liquid. This project explores that idea in the context of rare-earth pyrochlore compounds with mixed atomic species on the nonmagnetic metal/metalloid site. The level of random disorder can be controlled by the size mismatch of the different atomic species, allowing a systematic investigation of the influence of disorder on the formation of a quantum spin liquid or a related phase in disordered pyrochlore compounds. The goals are to develop guiding principles for utilizing disorder as a tool for stabilizing entangled magnetic states and evaluate the potential of disordered pyrochlores for achieving these states. The magnetic and structural properties of the materials are characterized by state-of-the-art techniques including x-ray and neutron total scattering, muon spin spectroscopy, and inelastic neutron scattering. This multi-modal methodological approach is ideally suited to gaining a comprehensive understanding of the local disorder and its effect on the magnetism in pyrochlore compounds, while also providing a template for similar studies on other materials in the future. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.