# Mainz 2017 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 29: Quantum Gases: Bosons IV

### Q 29.6: Vortrag

### Dienstag, 7. März 2017, 15:45–16:00, P 204

**A path-integral approach to composite, rotating impurities** — •Giacomo Bighin and Mikhail Lemeshko — Institute of Science and Technology Austria, Am Campus 1, 3400 Klosterneuburg, Austria

The study of composite, rotating impurities interacting with a quantum many-body environment is extremely important for the description of several experimental settings: cold molecules in a Bose-Einstein condensate or embedded in helium nanodroplets, electronic excitations in a BEC or in a solid. In all these cases the vibrational and rotational degrees of freedom create an involved energy level structure, with a continuous exchange of angular momentum with the surrounding environment. The recently-introduced angulon quasiparticle [1] formalises the concept of a rotating, interacting impurity. In this talk we introduce an alternative approach to the angulon problem making use of the path integral formalism, extending Feynman's treatment for the polaron. A clear advantage is that the bath degrees of freedom and the interaction can be integrated out exactly, resulting in an effective, single-particle description for the angulon in which the many-body character of the original problem is encoded in an interaction term. This alternative, effective treatment for the angulon is, in principle, valid at arbitrary coupling and at arbitrary temperature. The results obtained will be compared with existing state-of-the-art theories for composite impurities and with experimental data from the rotational spectrum of molecules embedded in helium nanodroplets.

References: [1] R. Schmidt and M. Lemeshko, Phys. Rev. Lett. 114, 203001 (2015) and Phys. Rev. X 6, 011012 (2016).