Collective quantum jumps of Rydberg atoms
  We study an open quantum system of atoms with long-range Rydberg interaction, laser driving, and spontaneous emission. Over time, the system occasionally jumps between a state of low Rydberg population and a state of high Rydberg population. The jumps are inherently collective and in fact exist only for a large number of atoms. We explain how entanglement and quantum measurement enable the jumps, which are otherwise classically forbidden. 
Tony E. Lee, H. H\"affner, M. C. Cross
cond-mat.quant-gas nlin.PS quant-ph