Condensed Matter Seminar: Disorder in order: Anderson localization in a randomless cold atom system

Félix Rose (MPQ)
Coupling a particle to the collective excitations of a system with many degrees of freedom radically alters the particle's properties.

Félix Rose (MPQ)
Online Seminar
Mon 27. April 2020, 11:30 am (MEZ)

Abstract:

Coupling a particle to the collective excitations of a system with many degrees of freedom radically alters the particle's properties. This paradigm, first proposed by Landau and Pekar to describe the coupling of electrons to lattice phonons giving rise to quasiparticles named polarons, has seen extensive use in the description of condensed matter systems.

In this presentation, I bring together the seemingly disconnected fields of polaron and disorder physics. Since Anderson realized that interference effects can hinder the diffusion of a particle to the point that it becomes localized, the interplay of disorder and quantum physics has been extensively studied, revealing other phenomena such as magnetoresistance or coherent backscattering.

After a brief review of (non-interacting) disorder physics, I will establish a mapping between the disorder-averaged motion of a particle evolving through a random scattering potential, and that of an impurity immersed in a disorder-free Bose-Einstein condensate (BEC). This gives a way to study the physics of disorder using a mass-imbalanced mixture of light fermionic impurities immersed in a bath of heavy bosons.

After having discussed the regime of validity of the mapping and possible extensions, I will apply the mapping to the one-dimensional case, where the time evolution of the impurity coupled to a BEC obtained via the approximate time-dependent variational method can be compared to the exact result in the corresponding disorder model, and discuss how different variational Ansätze can be thus compared.