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The Bose polaron - theory and experimental realisation

Georg Bruun (Aarhus University)
Onsdag, 7 december, 2016, at 16:15-17:00, in Aud. G1 (1532-116)
We investigate theoretically the properties of an impurity atom in a Bose-Einstein condensate (BEC). Using a systematic perturbation theory, we show that the energy of the impurity depends logarithmically on the scattering length to third order. When the boson-boson scattering length equals the boson-impurity scattering length, the energy has the same structure as that of a weakly interacting Bose gas, including terms of the Lee-Huang-Yang and fourth order logarithmic form. Using a variational approach, we show that the energy and residue of the polaron are significantly lowered by three-body correlations, even for weak interactions where there is no Efimov trimer state in a vacuum. Our theoretical results are compared with new radio-frequency spectroscopy data for impurity atoms in a BEC. The experiment demonstrates the existence of a long-lived quasi-particle state of the impurity, and there is excellent agreement between our theory and the experiment.
Kontaktperson: Jacob Schach Møller