Heidelberg 2015 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 32: Poster: Ultracold Atoms, Ions and BEC (with A)

Q 32.18: Poster

Tuesday, March 24, 2015, 17:00–19:00, C/Foyer

Polaronic effects in one- and two-band quantum systems — •Tao Yin, Daniel Cocks, Karla Baumann, and Walter Hofstetter — Institut für Theoretische Physik, Goethe-Universität, 60438 Frankfurt/Main, Germany

In this work we study the formation and dynamics of polarons in a system with a few latticed impurities immersed in a Bose-Einstein condensate (BEC). This system can be well described by a two-band model for the impurities, along with a Bogoliubov approximation for the BEC, with phonons coupled to impurities via both intra- and inter-band interaction. We decouple this Fröhlich-like coupling by an extended two-band Lang-Firsov polaron transformation using a variational method. The new effective Hamiltonian with two (polaron) bands differs from the original Hamiltonian by modified coherent transport, polaron energy shift and induced long-range interaction. Using Gutzwiller mean-field theory, we calculate the phase diagram and dynamics of this polaronic Hamiltonian in different dimension controlled by trapping lattice. An inhomogeneous system is also considered including BEC deformation from impurities, as well as a tilted optical lattice.

On the other hand, in order to focus on decoherence and relaxation effects, motivated by recent experiments, we specify our system as single impurity trapped in a quasi-1D system. Within a Lindblad master equation we take into account residual incoherent coupling between polaron and bath. Under this polaronic treatment, the inter-band relaxation process leads to a description of impurity dynamics beyond Fermi's Golden Rule.