Robust entanglement
  It is common belief among physicists that entangled states of quantum systems loose their coherence rather quickly. The reason is that any interaction with the environment which distinguishes between the entangled sub-systems collapses the quantum state. Here we investigate entangled states of two trapped Ca$^+$ ions and observe robust entanglement lasting for more than 20 seconds. 
H. Haeffner, F. Schmidt-Kaler, W. Haensel, C. F. Roos, T. Koerber, M.   Chwalla, M. Riebe, J. Benhelm, U. D. Rapol, C. Beche...