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Georg Bruun

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

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  • Nils B. Jørgensen
  • ,
  • Lars Wacker
  • ,
  • Kristoffer Theis Skalmstang, Danmark
  • Meera M. Parish, School of Physics & Astronomy, Monash University, Victoria 3800, Australi, Australien
  • Jesper Fredenslund Levinsen, Australien
  • Rasmus S. Christensen
  • ,
  • Georg M. Bruun
  • Jan J. Arlt
The behavior of a mobile impurity particle interacting with a quantum-mechanical medium is of fundamental importance in physics. Due to the great flexibility of atomic gases, our understanding of the impurity problem has improved dramatically since it was realized experimentally in a particularly pure form using degenerate Fermi gases. However, there has not been such a realization of the impurity problem in a bosonic reservoir so far. Here, we use radio frequency spectroscopy of ultracold bosonic $^{39}$K atoms to experimentally demonstrate the existence of a well-defined quasiparticle state for an impurity interacting with a Bose-Einstein condensate (BEC). We measure the energy of the impurity both for attractive and repulsive interactions with the BEC, and find excellent agreement with theories that incorporate three-body correlations, both in the weak-coupling limits and across unitarity. Our results show that the spectral response consists of a well-defined quasiparticle peak at weak coupling and a continuum of excited many-body states. For increasing interaction strength, the spectrum is strongly broadened and becomes dominated by the many-body continuum, but no significant effects of three-body decay are observed. Our results open up intriguing prospects for studying mobile impurities in a bosonic environment, as well as strongly interacting Bose systems in general.
TidsskriftPhysical Review Letters
Sider (fra-til)055302
Antal sider5
StatusUdgivet - 28 jul. 2016

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