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Q: Fachverband Quantenoptik und Photonik

Q 59: Ultra-cold atoms, ions and BEC IV (joint session A/Q)

Q 59.5: Vortrag

Donnerstag, 13. März 2025, 15:30–15:45, GrHS Mathe

Quasiparticle Properties of Long-range Impurities in a Bose Condensate — •Taha Alper Yogurt and Matthew Eiles — Max Planck Institute for the Physics of Complex Systems Nöthnitzer Straße 38 01187 Dresden

Atomic impurities inside of a Bose condensate facilitated the study of Fröhlich polarons, wherein impurity-bath interactions are considered only to linear order. The tunability of interactions enabled the exploration of attractive and repulsive polaron regimes, requiring interactions beyond Fröhlich (BF) model. In this regime, polaron dynamics intertwine with few-body physics, as short and long-range impurities support single or multiple bound states. Characterizing an impurity as a quasiparticle across various regimes and the determination of its quasiparticle properties have attracted significant interest. Here we employ two complementary methods to compute the quasiparticle properties of the contact, ion, and Rydberg impurities in the BF model. First, we use an ansatz in the form of a coherent state of the condensate excitations. The coherent-state amplitudes for zero momentum are calculated to determine the energy and quasiparticle weights, followed by solving the implicit equation for a moving impurity to obtain the effective mass. The second method treats the impurity as a slowly moving external potential and solves the Gross-Pitaevskii (GP) equation, assuming small perturbations around a uniform density. By expanding the GP energy in powers of the impurity velocity, we derive an analytical expression for the BF effective mass of the contact impurities, consistent with the former approach.

Keywords: Bose polarons; Ionic impurity; Rydberg polaron; Quasiparticle properties; Effective mass