Overview of the experiment. Panels (a) and (b) show the three-level Λ-type EIT systems for the storage of the signal light field, ε₊ and ε₋ denote right-circularly and left-circularly polarized signal light fields in a moderate magnetic field (B₀ = 12 Gs), respectively. The unit 1 Gs = 10^–4 T. C⁺ and C⁻ denote right-circularly and left-circularly components of the linearly polarized controlling light field, respectively. Panel (c) shows the experimental setup, where P: pump laser beam; BS: polarization-insensitive beam splitter; QWP_1,2: quarter-wave plates; C: linearly polarized controlling light (writing/reading) beam; OF: optical filters; PBS: polarization beam splitter.