Observation of Attractive and Repulsive Polarons in a Bose-Einstein Condensate

Nils B Jørgensen, Lars Wacker, Kristoffer T Skalmstang, Meera M Parish, Jesper Levinsen, Rasmus S Christensen, Georg M Bruun, Jan J Arlt

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216 Citations (Scopus)


The problem of an impurity particle moving through a bosonic medium plays a fundamental role in physics. However, the canonical scenario of a mobile impurity immersed in a Bose-Einstein condensate (BEC) has not yet been realized. Here, we use radio frequency spectroscopy of ultracold bosonic 39K atoms to experimentally demonstrate the existence of a well-defined quasiparticle state of an impurity interacting with a BEC. We measure the energy of the impurity both for attractive and repulsive interactions, and find excellent agreement with theories that incorporate three-body correlations, both in the weak-coupling limits and across unitarity. The spectral response consists of a well-defined quasiparticle peak at weak coupling, while for increasing interaction strength, the spectrum is strongly broadened and becomes dominated by the many-body continuum of excited states. Crucially, no significant effects of three-body decay are observed. Our results open up exciting prospects for studying mobile impurities in a bosonic environment and strongly interacting Bose systems in general.

Original languageEnglish
Article number055302
Pages (from-to)1-6
Number of pages6
JournalPhysical Review Letters
Issue number5
Publication statusPublished - 28 Jul 2016

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