A heralded quantum memory scheme with high storage-retrieve efficiency*

The faithful storage and retrieval of a quantum bit of light is of fundamental importance for quantum communication, quantum networking and quantum computation. Here, we demonstrate a heralded quantum memory scheme in an atomic optical cavity system with both high storage and retrieval efficiency. A 3\% total storage-retrieval efficiency is reached by using a coherent pulse, which is around 10000 times higher than experiment previously presented \footnote{Tanji, H. and Ghosh, Phys. Rev. Lett. \textbf{103}, 043601 (2009)}. Replacing the coherent pulse with a heralded single photon produced from four-wave mixing \footnote{B. Srivathsan and G. K. Gulati, Phys. Rev. Lett. \textbf{111},123602 (2013)}, we demonstrate a storage efficiency of 0.92\%. This is an important step towards realizing a high-efficiency heralded quantum memory for a single photon.