  Quantum memories with high efficiency and fidelity are essential for
long-distance quantum communication and information processing. Techniques have
been developed for quantum memories based on atomic ensembles. The atomic
memories relying on the atom-light resonant interaction usually suffer from the
limitations of narrow bandwidth. The far-off-resonant Raman process has been
considered a potential candidate for use in atomic memories with large
bandwidths and high speeds. However, to date, the low memory efficiency remains
an unsolved bottleneck. Here, we demonstrate a high-performance atomic Raman
memory in Rb87 vapour with the development of an optimal control technique. A
memory efficiency of 82.6% for 10-ns optical pulses is achieved and is the
highest realized to date in atomic Raman memories. In particular, an
unconditional fidelity of up to 98.0%, significantly exceeding the no-cloning
limit, is obtained with the tomography reconstruction for a single-photon level
coherent input. Our work marks an important advance of atomic Raman memory
towards practical applications in quantum information processing.
