SAMOP 2023 – scientific programme
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A: Fachverband Atomphysik
A 27: Poster III
A 27.24: Poster
Thursday, March 9, 2023, 16:30–19:00, Empore Lichthof
Extended Mean-field Theory of strong coupling Bose polarons — •Nader Mostaan1, Nathan Goldman2, and Fabian Grusdt1 — 1Department of Physics and Arnold Sommerfeld Center for Theoretical Physics (ASC), Ludwig-Maximilians-Universität München, Theresienstr. 37, D-80333 München, Germany. Munich Center for Quantum Science and Technology (MCQST), Schellingstr. 4, D-80799 München, Germany. — 2CENOLI, Universite Libre de Bruxelles, CP 231, Campus Plaine, B-1050 Brussels, Belgium.
A mobile quantum impurity resonantly coupled to a BEC forms a quasiparticle termed Bose polaron. In cold atom realizations of Bose polaron, the strength of the impurity-boson interactions is tunable via Feshbach resonances. At strong coupling, when an impurity-boson dimer exists, an unstable collective mode exists on top of the mean-field solution; thus, the impurity can bind a diverging number of non-interacting bosons. In this case, inter-boson interactions are crucial to stabilizing the Bose polaron. To describe Bose polaron, we employ an extension of coherent state variational ansatz, which accounts for beyond mean-field correlations of the bound mode. We find that the state of the bound mode is well described by a Fock-coherent state, and the impurity-boson resonance is shifted as a result of screening by the bosons bound to the impurity. In addition, we identify first-order phase transitions between Fock states with increasing occupation numbers. Our results corroborate the existence of multibody resonances between the attractive and repulsive polaron branches, which can be experimentally detected using impurity spectroscopy techniques.