Response to comment by Tin-Lun Ho on "Itinerant Ferromagnetism in a Strongly Interacting Fermi Gas of Ultracold Atoms", Science 325, 1521 (2009)

TL;DR

This paper defends the original experimental evidence for itinerant ferromagnetism in ultracold Fermi gases against a comment claiming the evidence is invalid, clarifying the interpretation of the results and emphasizing the need for further experiments.

Contribution

It provides a rebuttal to a critique by clarifying the validity of the original experimental evidence for ferromagnetism in ultracold Fermi gases.

Findings

Experimental evidence is consistent with ferromagnetism.

Critique based on invalid relaxation time estimates.

Further experiments are necessary to confirm ferromagnetic ground state.

Abstract

Ho claims in his comment that our experiment is direct evidence that itinerant ferromagnetism does not exist in ultracold Fermi gases. This claim is incorrect and based on an invalid estimate of relaxation times and an erroneous interpretation of the detectability of ferromagnetic domains. We point out that the experimental evidence is consistent with the existence of ferromagnetism, but further experiments are needed to distinguish a ferromagnetic ground state from a non-magnetic ground state with ferromagnetic correlations.