Creation of Rydberg Polarons in a Bose Gas

In this talk we review the theory of various types of Bose polarons that can be realized in ultracold atomic systems. We then report the spectroscopic observation of Rydberg polarons in a Bose gas which is in excellent agreement with theoretical predictions [1]. This novel type of polaron is created by excitation of Rydberg atoms in a strontium Bose-Einstein condensate and it is distinguished by the occupation of a large number bound molecular states [2]. The cross-over from few-body bound molecular oligomers to many-body polaron features is described with a functional determinant theory that solves an extended Froehlich Hamiltonian for an impurity in a Bose gas. The detailed analysis of the red-detuned tail of the excitation spectrum describes the contribution from the region of highest density in the condensate and provides a clear signature of Rydberg polarons. This work [1] has been performed in collaboration with groups at Rice University, Harvard University, and the TU Vienna.\\ \newline References:\\ [1] F. Camargo, R. Schmidt, J. D. Whalen, R. Ding, G. Woehl Jr., S. Yoshida, J. Burgd\"{o}rfer, F. B. Dunning, H. R. Sadeghpour, E. Demler, and T. C. Killian, in preparation (2017).\\ [2] R. Schmidt, H. R. Sadeghpour, and E. Demler, Phys. Rev. Lett. 116, 105302 (2016).