  We interface a spontaneous parametric down conversion (SPDC) crystal and a
cold atomic ensemble and demonstrate a highly efficient quantum memory through
polarization-encoded single-photon qubits. Specifically, narrowband heralded
single photons from a cavity-enhanced SPDC source is stored using cold atomic
ensemble, with ~70% storage-and-retrieval efficiency and ~10$\mu$s storage time
at 50% efficiency. To prevent the degradation after storage, we also manipulate
the single-photon wave profile so that the retrieved non-classical nature of
single photon is preserved. On the other hand, the dual-rail storage is used
for storing polarization-encoded qubits, and the corrected fidelity of flying
qubits after storage reaches ~97%. The results pave the way toward large-scale
quantum network.
