High Storage Efficiency and Large Fractional Delay of EIT-Based Memory

In long-distance quantum communication and optical quantum computation, an efficient and long-lived quantum memory is an important component. We first experimentally demonstrated that a time-space-reversing method plus the optimum pulse shape can improve the storage efficiency (SE) of light pulses to 78{\%} in cold media based on the effect of electromagnetically induced transparency (EIT). We obtain a large fractional delay of 74 at 50{\%} SE, which is the best record so far. The measured classical fidelity of the recalled pulse is higher than 90{\%} and nearly independent of the storage time, implying that the optical memory maintains excellent phase coherence. Our results suggest the current result may be readily applied to single-photon quantum states due to quantum nature of the EIT light-matter inference. This study advances the EIT-based quantum memory in practical quantum information applications.