Thermal properties of quantum gases

Christophe Salomon

Yijun Tang, A. G. Sykes, Nathaniel Burdick +3 more

We report on the anisotropic expansion of ultracold bosonic dysprosium gases at temperatures above quantum degeneracy and develop a quantitative theory to describe this behavior. The theory expresses the postexpansion aspect ratio in terms of temperature and microscopic collisional properties by incorporating Hartree-Fock mean-field interactions, hydrodynamic effects, and Bose-enhancement factors. Our results extend the utility of expansion imaging by providing accurate thermometry for dipolar thermal Bose gases. Furthermore, we present a simple method to determine scattering lengths in dipolar gases, including near a Feshbach resonance, through observation of thermal gas expansion.

H. Schmaljohann, M. Erhard, J. Kronjägert +5 more

We study the static and dynamic magnetic properties of ultracold quantum gases, in particular the spinor physics of F = 1 and F = 2 Bose-Einstein condensates of 87Rb atoms. Our data lead to the conclusion, that the F = 2 ground state of 87Rb is polar, while we find the F = 1 ground state to be ferromagnetic. The dynamics of spinor systems is linked to an interplay between coherent mean-field interactions, losses and interactions with atoms in the thermal cloud. Within this rich parameter space we observe indications for coherent spinor dynamics and novel thermalization regimes.

Peter O. Fedichev, A. E. Muryshev

We develop a theory of equilibrium properties and dissipative dynamics of large vortex arrays in trapped Bose-condensed gases. We prove that, in spite of the spatial inhomogeneity of the condensate density profile in trapped gases, the equilibrium configuration corresponds to a vortex array of uniform density. We show that in a static trap the interaction of the vortex array with thermal excitations leads to a nonexponential decay of the vortex structure, and the characteristic lifetime depends on the initial density of vortices. Drawing an analogy with physics of pulsars, we propose an experiment that employs the decay induced heating of the thermal cloud as a tool for a nondestructive study of the vortex dynamics.

V. V. Ul'yanov, S. S. Sokolov