Quench Dynamics and Orthogonality Catastrophe of Bose Polarons

25 September 2019

Photo: AG Schmelcher

Mobile impurities immersed in a surrounding quantum many-body environment are dressed by the collective excitation of the latter forming quasiparticles such as polarons (see the left panel of Fig. 1). This dressing mechanism results to alterations of the fundamental impurity properties, such as their effective mass and induced interactions as well as dramatic changes during their nonequilibrium dynamics.

In the current work, we unravel the correlated quench induced dynamical dressing of a spinor impurity repulsively interacting with a Bose-Einstein condensate. Inspecting the temporal evolution of the impurity’s spin polarization (contrast) we expose the emergence of three distinct dynamical regions for varying impurity-BEC interspecies interaction (see middle panel of Fig. 1). These regions signify the birth, dynamical deformation and death of repulsive Bose polarons and are found to be related to the ohmic character of the bath. A key result of our research is the breakdown of the polaron picture for strong interactions via its orthogonality catastrophe. Indeed, in this strongly interacting regime a dissipative motion of the impurity is observed (right panel of Fig. 1) accompanied by the population of several lower-lying excited states. Moreover, this dissipation mechanism leads to a transfer of energy from the impurity to its host, signaling also the presence of entanglement in the many-body system.

Physical Review Letters 122, 183001 (2019).