# CQD Special Seminar

### 13. December 2017 14:00

Seminarraum, Institut für Theoretische Physik, Philosophenweg 19### Soliton friction and pairing in superfluids

**Dr. Johannes Hofmann**

Cambridge University, United Kingdom

I shall discuss two examples of interaction effects in quantum gases.

First, I shall discuss the interaction of a collective quantum object - a soliton in a one-dimensional Bose gas - with its thermal environment. Intuitively, one could think of this object as a large pollen in a fluid, expecting Brownian motion to affect the soliton dynamics. Yet, because of the underlying integrability of the problem, it was long thought that such an interaction does not exist. It turns out, however, that there remains a more subtle interplay between soliton and thermal gas which gives rise to a damping force similar to the radiation force exerted on an accelerated charge in electrodynamics, called the Abraham-Lorentz force.

The second part of the talk will discuss interaction effects in mesoscopic Fermi gases relevant to ongoing experiments in Heidelberg as well as experiments on SrTiO3 nanostructures. While Fermi gases with a variable interaction typically realize a BEC-BCS crossover, finite particle number or confinement can give rise to additional fluctuation effects. I will introduce some aspects of mesoscopic superfluids and discuss how fluctuation effects show up in experiments.

Finite temperature simulations of false vacuum decay in a spin-1 Bose gas

*Dr. Kate Brown, School of Mathematics, Statistics and Physics, Newcastle University, Newcastle upon Tyne, UK*, Physikalisches Institut, INF 226, K 1-3