Relaxation of the Collective Magnetization of a Dense 3D Array of Interacting Dipolar S=3 Atoms.

We report on measurements of the dynamics of the total magnetization and spin populations in an almost unit-filled lattice system comprising about 10^{4} spin S=3 chromium atoms, under the effect of dipolar interactions. The observed spin population dynamics is unaffected by the use of a spin echo and fully consistent with numerical simulations of the S=3 XXZ spin model. On the contrary, the observed magnetization decays slower than in simulations and, surprisingly, reaches a small but nonzero asymptotic value within the longest timescale. Our findings show that spin coherences are sensitive probes to systematic effects affecting quantum many-body behavior that cannot be diagnosed by merely measuring spin populations.