  Long-lived storage of arbitrary transverse multimodes is important for
establishing a high-channel-capacity quantum network. Most of the pioneering
works focused on atomic diffusion as the dominant impact on the retrieved
pattern in an atom-based memory. In this work, we demonstrate that the
unsynchronized Larmor precession of atoms in the inhomogeneous magnetic field
dominates the distortion of the pattern stored in a cold-atom-based memory. We
find that this distortion effect can be eliminated by applying a strong uniform
polarization magnetic field. By preparing atoms in magnetically insensitive
states, the destructive interference between different spin-wave components is
diminished, and the stored localized patterns are synchronized further in a
single spin-wave component; then, an obvious enhancement in preserving patterns
for a long time is obtained. The reported results are very promising for
studying transverse multimode decoherence in storage and high-dimensional
quantum networks in the future.
