Detecting multiparticle entanglement of Dicke states
  Recent experiments demonstrate the production of many thousands of neutral atoms entangled in their spin degrees of freedom. We present a criterion for estimating the amount of entanglement based on a measurement of the global spin. It outperforms previous criteria and applies to a wide class of entangled states, including Dicke states. Experimentally, we produce a Dicke-like state using spin dynamics in a Bose-Einstein condensate. Our criterion proves that it contains at least genuine 28-particle entanglement. We infer a generalized squeezing parameter of -11.4(5) dB. 
Bernd L\"ucke, Jan Peise, Giuseppe Vitagliano, Jan Arlt, Luis Santos,   Geza Toth, Carsten Klempt
quant-ph cond-mat.quant-gas