Condensed Matter Seminar: Rotational cooling of a Molecule in a BEC and strong interacting Bose polarons in 1D

Martin Will (University of Kaiserslautern)
Online Seminar
Mon 23. November 2020, 11:30 am (MEZ)

Abstract:
In the first part of the talk I will discuss the rotational cooling of homonuclear diatomic molecules in a Bose-Einstein-condensate (BEC). For typical molecules there is no frictionless rotation since the dominant cooling occurs via emission of particle-like phonons. Only for macro-dimers, whose size becomes larger than the condensate healing length, a Landau-like, critical angular momentum exists below which phonon emission is suppressed. We analyze the dynamics of rotational cooling for homo-nuclear diatomic molecules based on a quantum Boltzmann equation including single- and two-phonon scattering. For typical molecules two-phonon scattering becomes relevant at finite temperature.
In the second part I discuss the interaction of a quantum impurity with a one-dimensional degenerate Bose gas forming a Bose polaron. In three spatial dimension, the quasiparticle is typically well described by the extended Fröhlich model. This description, which assumes an undepleted condensate, fails however in 1D, where the back action of the impurity on the condensate leads to a self-bound mean-field polaron for arbitrarily weak impurity-boson interactions. I present a model that takes into account this back action and describes the impurity-condensate interaction as coupling to phonon like excitations of a deformed condensate.