Spatial multiplexing of atom-photon entanglement sources using   feed-forward controls and switching networks
  The light-matter quantum interface that can create quantum-correlations or entanglement between a photon and one atomic collective excitation is a fundamental building block for a quantum repeater. The intrinsic limit is that the probability of preparing such non-classical atom-photon correlations has to be kept low in order to suppress multi-excitation. To enhance this probability without introducing multi-excitation errors, a promising scheme is to apply multimode memories into the interface. Significant progresses have been made in temporal, spectral, and spatial multiplexing memories, but the enhanced probability for generating the entangled atom-photon pair has not been experimentally realized. Here, by using 6 spin-wave-photon entanglement sources, a switching network and feed-forward control, we build a multiplexed light-matter interface and then demonstrate a ~6-fold (~4-fold) probability increase in generating entangled atom-photon (photon-photon) pairs. The measured compositive Bell parameter for the multiplexed interface is 2.49+-0.03 combined with a memory lifetime of up to ~60 microseconds. 
Long Tian, Zhongxiao Xu, Lirong Chen, Wei Ge, Haoxiang Yuan, Yafei   Wen, Shengzhi Wang, Shujing Li and Hai Wang
quant-ph