  In this paper we report an experiment that verifies an atomic-ensemble
quantum memory via a measurement-device-independent scheme. A single photon
generated via Rydberg blockade in one atomic ensemble is stored in another
atomic ensemble via electromagnetically induced transparency. After storage for
a long duration, this photon is retrieved and interfered with a second photon
to perform joint Bell-state measurement (BSM). Quantum state for each photon is
chosen based on a quantum random number generator respectively in each run. By
evaluating correlations between the random states and BSM results, we certify
that our memory is genuinely entanglement-preserving.
