Mainz 2026 – wissenschaftliches Programm

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Q: Fachverband Quantenoptik und Photonik

Q 24: Ultra-cold Atoms, Ions and BEC I (joint session A/Q)

Q 24.2: Vortrag

Dienstag, 3. März 2026, 11:15–11:30, N 1

Mass-Gap Description of Heavy Impurities in Fermi Gases — Xin Chen, •Eugen Dizer, Emilio Ramos Rodríguez, and Richard Schmidt — Institut für Theoretische Physik, Universität Heidelberg, 69120 Heidelberg, Germany

Single impurities immersed in a degenerate Fermi gas exhibit fascinating many-body phenomena, such as the polaron-to-molecule transition and Anderson's orthogonality catastrophe (OC). It is known that mobile impurities of finite mass can be described as quasiparticles, so called Fermi polarons. In contrast, Anderson showed in 1967 that the ground state of a static, infinitely heavy impurity in a Fermi sea is orthogonal to the ground state of the system without impurity - a hallmark of the OC and a fundamentally non-perturbative effect. As a result, conventional variational approaches or path integral methods fail to capture this phenomenon accurately. Despite decades of research, a unified approach connecting the quasiparticle description of Fermi polarons with Anderson's OC has remained elusive. In this work, we present a theoretical framework for arbitrary-mass impurities in a Fermi sea that incorporates Anderson's OC, the polaron-to-molecule transition and the quasiparticle picture. Our theory provides a simple yet powerful description of interacting quantum systems, with broad implications for ultracold atom experiments, atomically thin semiconductors, and future studies of strongly correlated matter. Phys. Rev. Lett. 135, 193401 (2025).

Keywords: Polaron Physics; Anderson's Orthogonality Catastrophe; Mean-Field Theory; Exact Diagonalization; Quasiparticles