Abstract
In this paper we consider a recent experiment [Phys. Rev. A 95, 053638 (2017)] in which an antiferromagnetic spin-1 condensate of Na-23 atoms was quenched from the easy-axis polar phase into the easy-plane polar phase. We simulate the phase-transition dynamics by using a classical field method with noisy initial conditions and find good agreement with the experimental observations. We analyze the late-time dynamics in terms of phase ordering by using the nematic order parameter that we have developed in earlier work [Phys. Rev. A 96, 013602 (2017)]. We show that these experiments are able to explore the early stages of universal phase ordering where the domains grow diffusively.