In situ determination of Zeeman content of collective atomic memories

Knowledge and control of atomic Zeeman populations is necessary for the realization of useful, long-lived quantum memories. We propose and implement a method to determine atomic state population distributions for atomic spin waves. Zeeman composition of single atomic spin waves of a cold atomic gas, confined in a one-dimensional optical lattice, is inferred with high precision by measurements of signal-idler polarization correlations as a function of spin-wave storage time.