Non-equilibrium Dynamics of Topological Excitations: from Quantum Materials to Quantum Information

• Applicant: Dr. Aprem Joy
• Subject Area: Theoretical Condensed Matter Physics
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 574865650

In modern condensed matter physics, the interplay between quantum entanglement and topological phases gives rise to a wealth of novel emergent phenomena. A striking example is the emergence of gauge theories and quasiparticles with fractional quantum numbers and non-trivial exchange statistics—anyons. Yet, unambiguously detecting topological phases and anyons in quantum materials remains one of the central challenges in the field. During my Ph.D., I advanced this line of research by investigating the paradigmatic Kitaev spin liquid, formulating a comprehensive theory of its emergent dynamical gauge field and anyonic excitations in experimentally relevant models. For my postdoctoral phase, I aim to build on these insights to propose novel ways to detect fractionalized phases and anyons, simultaneously broaden my expertise by exploring their fascinating interplay with quantum information.In the first part of my proposal, I introduce a new class of experimental probes tailored to a broad range of quantum materials. These are designed to detect topological order through the dimensional constraints on fundamental excitations. The core idea is that in layered 3D materials hosting 2D topological phases, elementary excitations are topologically confined to move within individual layers. Their motion into the bulk requires the interaction of at least two excitations—a behavior fundamentally distinct from non-topological systems, where single quasiparticles are free to move in all three dimensions. To detect this emergent constraint, I propose and theoretically investigate a pump-probe scheme in which a laser pulse generates a high density of quasiparticles at the surface, and a subsequent probe laser monitors their relaxation dynamics.The second part of my proposal explores the quantum information-theoretic aspects of equilibration in topological phases. Specifically, the non-Abelian nature of anyons leads to an intricate relationship between quantum information—encoded in their internal states—and their real-space dynamics. I aim to investigate this interplay using tools from quantum information theory, also addressing questions that arise in the first part of the project.The proposal outlines a detailed plan to: (i) model the equilibration of anyonic quasiparticles using exact simulations and hydrodynamic equations; (ii) study the effects of disorder and impurities on their dynamics; (iii) propose optical techniques to monitor anyon densities; and (iv) construct quantum circuit models to study the evolution of quantum information during equilibration.Overall, this proposal presents a novel and robust approach to probing topological quantum spin liquid phases and anyonic quasiparticles in a broad class of quantum materials, while also shedding light on the fundamental interplay between non-equilibrium dynamics and quantum information in topological matter.

• DFG Programme: Fellowship
• International Connection: USA
• Host: Professor Leon Balents, Ph.D.