Quantum dense coding via atomic ensembles without prior distributed   entangled state
  We investigate a scheme for implementing quantum dense coding via atomic ensembles, where prior distribution of the quantum entangled state is not needed. Our scheme also combines another two distinct advantages: atomic ensembles qubits with long coherent time serve as memory qubits and phtonic qubit as flying qubit. Thus our suggestion may offer a simple and easy way of demonstrating quantum dense coding experimentally via atomic ensembles. 
Zheng-Yuan Xue, Ping Dong, Ming Yang, You-Min Yi, Zhuo-Liang Cao