Entanglement of orbital angular momentum states between an ensemble of   cold atoms and a photon
  Recently, atomic ensemble and single photons were successfully entangled by using collective enhancement [D. N. Matsukevich, \textit{et al.}, Phys. Rev. Lett. \textbf{95}, 040405(2005).], where atomic internal states and photonic polarization states were correlated in nonlocal manner. Here we experimentally clarified that in an ensemble of atoms and a photon system, there also exists an entanglement concerned with spatial degrees of freedom. Generation of higher-dimensional entanglement between remote atomic ensemble and an application to condensed matter physics are also discussed. 
R. Inoue, N. Kanai, T. Yonehara, Y. Miyamoto, M. Koashi and M. Kozuma