Ehud Altman Abstract

Ehud Altman

"Non equilibrium Ferromagnetism and Stoner transition in an ultracold Fermi gas"

Abstract:

Experiments with ultracold Fermi gases at MIT performed on the "repulsive" side of a Feshbach resonance show dramatic effects, which could be seen as evidence for a transition to a ferromagnet. This interpretation is complicated however by the fact that the repulsive Fermi gas is only a meta-stable state in which the true low energy objects, the bound Feshbach molecules, are initially unoccupied. Interactions allow for gradual decay into these bound molecular states, which is seen in the experiments as a constant loss of atoms. I will argue that besides the obvious classical effect of loss there is an interesting quantum effect. The loss gives rise to an effective dissipative interaction that damps quantum fluctuations and thereby changes the nature of the Ferromagnetic transition in a way that may explain certain puzzles in the experimental results.

I also propose an experimental scheme to study magnetic phenomena in a repulsive Fermi gas which alleviates the problem of loss. The idea is to prepare the system in a nearly ferromagnetic spin spiral and observe the ensuing dynamic instabilities. I will show how the dynamical modes change when the interaction is tuned across the Ferromagnetic transition.

BIO: PhD at the Technion with Prof. Assa Auerbach on superconductivity and quantum magnetism, and a bit of cold atoms. Postdoc at Harvard, worked mainly on ultracold atoms Now faculty member (Tenure track) at the Weizmann institute