Control of dark-state polariton collapses in a doped crystal

We investigate light storage by electromagnetically induced transparency in a Pr3+:Y2SiO5 crystal. The retrieval efficiency versus storage time shows pronounced oscillations, which are due to beating of dark-state polaritons in multiple Zeeman-shifted Λ systems. As a significant obstacle for applications, the beating leads to periodic collapses of the retrieved signal. We demonstrate how to systematically control the perturbing oscillations in the retrieval efficiency by external magnetic fields. This enables suppression of collapses and retrieval of stored data at any storage time, approaching the limit set by the coherence time in the medium.