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Q: Fachverband Quantenoptik und Photonik
Q 51: Ultra-cold Atoms, Ions and BEC III (joint session A/Q)
Q 51.4: Talk
Thursday, March 5, 2026, 12:00–12:15, N 1
Spectroscopic structure of the heavy Fermi polaron — •Michael Rautenberg1, Tobias Krom1, Eugen Dizer2, Olivier Bleu2, Richard Schmidt2, Tilman Enss2, Lauriane Chomaz1, and Matthias Weidemüller1 — 1Physikalisches Institut, Heidelberg University — 2Institut für Theoretische Physik, Heidelberg University
I am going to present our latest spectroscopic measurements on the structure of the heavy Fermi polaron. In our experiment, this system is realized by a few heavy Caesium (133Cs) impurities immersed in a deeply degenerate Fermi gas of much lighter Lithium (6Li) atoms.
While Fermi polarons - quasiparticles formed by impurities dressed by the excitations of a surrounding Fermi sea - are interesting in their own right, the large mass ratio in the Li-Cs system additionally enables addressing questions about the fate of quasiparticles close to the infinitely heavy impurity limit. At this point, Landau’s quasiparticle picture [1] breaks down and the system is best described by a new state that is fully orthogonal to the Fermi sea without the impurity - a phenomenon dubbed “Anderson orthogonality catastrophe” [2].
Using tuneable impurity-bath interactions close to a magnetic Li-Cs Feshbach resonance, we can investigate both ground and excited states of the polaron using spectroscopy between two Cs hyperfine states. A careful comparison to different theoretical models sheds light onto the effects of finite temperature and finite mass of the heavy Fermi polaron.
[1] L. D. Landau, Phys. Z. Sowjetunion, 3:644 (1933)
[2] P. W. Anderson, Phys. Rev. Lett. 18, 1049-1051 (1967)
Keywords: polaron; Fermi polaron; Anderson orthogoality catastrophe; spectroscopy; quasiparticle